kernel/vm: fix several vm bugs in riscv64

team.cpp address_space change is needed in
arch_thread_init_kthread_stack to set initial thread page
translation map. It also allows to simplify some debugger code.

DEBUG_PAGE_ACCESS check is currently incorrectly implemented in
RISCV64VMTranslationMap and disabled to avoid panic.

gHtifRegs = 0 change is needed to avoid using HTIF when it is not
available. gHtifRegs != NULL check is used to detect that HTIF is
present. 0x40008000 is TinyEMU HTIF address. HTIF is emulator specific
device that provide serial IO and shutdown capability (and maybe
something else depending on virtual machine).

Change-Id: Ic4d567b28c49799ae0f55223dd983a752823bab4
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4328
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>

kernel/arch/platform: implement for riscv64

Change-Id: Id1839ef39d927e6a2017c8b8ac3482d9eeb00fa1
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4059
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>

riscv64: Fill in more bulk architecture items around libroot/kernel

Change-Id: Ia2a86d8814d06950ea2d2d19d966c642d26f81d6
Reviewed-on: https://review.haiku-os.org/c/1302
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>