MIPS: SGI-IP22: Remove unnecessary check of GCC option

According to Documentation/process/changes.rst, the minimal version of GCC
is 5.1, and -mr10k-cache-barrier=store is supported with GCC 5.1 [1], just
remove the unnecessary check to fix the build error [2]:

arch/mips/sgi-ip22/Platform:28: *** gcc doesn't support needed option -mr10k-cache-barrier=store. Stop.

[1] https://gcc.gnu.org/onlinedocs/gcc-5.1.0/gcc/MIPS-Options.html
[2] https://github.com/ClangBuiltLinux/linux/issues/1543

Reported-by: Ryutaroh Matsumoto <ryutaroh@ict.e.titech.ac.jp>
Suggested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

MIPS: Only include the platform file needed

Instead of including all Platform files, we simply include the
needed one and avoid clashes with makefile variables.

Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

MIPS: ip22: Fix ip28 build for modern gcc

kernelci reports a failure of the ip28_defconfig build after upgrading its
gcc version:

arch/mips/sgi-ip22/Platform:29: *** gcc doesn't support needed option -mr10k-cache-barrier=store. Stop.

The problem apparently is that the -mr10k-cache-barrier=store option is now
rejected for CPUs other than r10k. Explicitly including the CPU in the
check fixes this and is safe because both options were introduced in
gcc-4.4.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/15049/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

MIPS: IP22, IP28: Migrate to new platform makefile style.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>