arch: vdso: consolidate gettime prototypes

The VDSO functions are defined as globals in the kernel sources but intended
to be called from userspace, so there is no need to declare them in a kernel
side header.

Without a prototype, this now causes warnings such as

arch/mips/vdso/vgettimeofday.c:14:5: error: no previous prototype for '__vdso_clock_gettime' [-Werror=missing-prototypes]
arch/mips/vdso/vgettimeofday.c:28:5: error: no previous prototype for '__vdso_gettimeofday' [-Werror=missing-prototypes]
arch/mips/vdso/vgettimeofday.c:36:5: error: no previous prototype for '__vdso_clock_getres' [-Werror=missing-prototypes]
arch/mips/vdso/vgettimeofday.c:42:5: error: no previous prototype for '__vdso_clock_gettime64' [-Werror=missing-prototypes]
arch/sparc/vdso/vclock_gettime.c:254:1: error: no previous prototype for '__vdso_clock_gettime' [-Werror=missing-prototypes]
arch/sparc/vdso/vclock_gettime.c:282:1: error: no previous prototype for '__vdso_clock_gettime_stick' [-Werror=missing-prototypes]
arch/sparc/vdso/vclock_gettime.c:307:1: error: no previous prototype for '__vdso_gettimeofday' [-Werror=missing-prototypes]
arch/sparc/vdso/vclock_gettime.c:343:1: error: no previous prototype for '__vdso_gettimeofday_stick' [-Werror=missing-prototypes]

Most architectures have already added workarounds for these by adding
declarations somewhere, but since these are all compatible, we should
really just have one copy, with an #ifdef check for the 32-bit vs
64-bit variant and use that everywhere.

Unfortunately, the sparc an um versions are currently incompatible
since they never added support for __vdso_clock_gettime64() in 32-bit
userland. For the moment, I'm leaving this one out, as I can't
easily test it and it requires a larger rework.

Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

csky: Fixup -Wmissing-prototypes warning

Cleanup the warnings:

arch/csky/kernel/ptrace.c:320:16: error: no previous prototype for 'syscall_trace_enter' [-Werror=missing-prototypes]
arch/csky/kernel/ptrace.c:336:17: error: no previous prototype for 'syscall_trace_exit' [-Werror=missing-prototypes]
arch/csky/kernel/setup.c:116:34: error: no previous prototype for 'csky_start' [-Werror=missing-prototypes]
arch/csky/kernel/signal.c:255:17: error: no previous prototype for 'do_notify_resume' [-Werror=missing-prototypes]
arch/csky/kernel/traps.c:150:15: error: no previous prototype for 'do_trap_unknown' [-Werror=missing-prototypes]
arch/csky/kernel/traps.c:152:15: error: no previous prototype for 'do_trap_zdiv' [-Werror=missing-prototypes]
arch/csky/kernel/traps.c:154:15: error: no previous prototype for 'do_trap_buserr' [-Werror=missing-prototypes]
arch/csky/kernel/traps.c:157:17: error: no previous prototype for 'do_trap_misaligned' [-Werror=missing-prototypes]
arch/csky/kernel/traps.c:168:17: error: no previous prototype for 'do_trap_bkpt' [-Werror=missing-prototypes]
arch/csky/kernel/traps.c:187:17: error: no previous prototype for 'do_trap_illinsn' [-Werror=missing-prototypes]
arch/csky/kernel/traps.c:210:17: error: no previous prototype for 'do_trap_fpe' [-Werror=missing-prototypes]
arch/csky/kernel/traps.c:220:17: error: no previous prototype for 'do_trap_priv' [-Werror=missing-prototypes]
arch/csky/kernel/traps.c:230:17: error: no previous prototype for 'trap_c' [-Werror=missing-prototypes]
arch/csky/kernel/traps.c:57:13: error: no previous prototype for 'trap_init' [-Werror=missing-prototypes]
arch/csky/kernel/vdso/vgettimeofday.c:12:5: error: no previous prototype for '__vdso_clock_gettime64' [-Werror=missing-prototypes]
arch/csky/kernel/vdso/vgettimeofday.c:18:5: error: no previous prototype for '__vdso_gettimeofday' [-Werror=missing-prototypes]
arch/csky/kernel/vdso/vgettimeofday.c:24:5: error: no previous prototype for '__vdso_clock_getres' [-Werror=missing-prototypes]
arch/csky/kernel/vdso/vgettimeofday.c:6:5: error: no previous prototype for '__vdso_clock_gettime' [-Werror=missing-prototypes]
arch/csky/mm/fault.c:187:17: error: no previous prototype for 'do_page_fault' [-Werror=missing-prototypes]

Link: https://lore.kernel.org/lkml/20230810141947.1236730-17-arnd@kernel.org/
Reported-by: Arnd Bergmann <arnd@kernel.org>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>

csky: Add VDSO with GENERIC_GETTIMEOFDAY, GENERIC_TIME_VSYSCALL, HAVE_GENERIC_VDSO

It could help to reduce the latency of the time-related functions
in user space.

We have referenced arm's and riscv's implementation for the patch.

Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Cc: Vincent Chen <vincent.chen@sifive.com>
Cc: Arnd Bergmann <arnd@arndb.de>