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>

arch/mips/sgi-ip22/Platform

@@ -23,10 +23,5 @@ endif
 # be 16kb aligned or the handling of the current variable will break.
 # Simplified: what IP22 does at 128MB+ in ksegN, IP28 does at 512MB+ in xkphys
 #
-ifdef CONFIG_SGI_IP28
-  ifeq ($(call cc-option-yn,-march=r10000 -mr10k-cache-barrier=store), n)
-      $(error gcc doesn't support needed option -mr10k-cache-barrier=store)
-  endif
-endif
 cflags-$(CONFIG_SGI_IP28)	+= -mr10k-cache-barrier=store -I$(srctree)/arch/mips/include/asm/mach-ip28
 load-$(CONFIG_SGI_IP28)		+= 0xa800000020004000