MIPS: Move '-Wa,-msoft-float' check from as-option to cc-option

This patch is for linux-6.1.y and earlier, it has no direct mainline
equivalent.

In order to backport commit d5c8d6e ("kbuild: Update assembler
calls to use proper flags and language target") to resolve a separate
issue regarding PowerPC, the problem noticed and fixed by
commit 80a20d2 ("MIPS: Always use -Wa,-msoft-float and eliminate
GAS_HAS_SET_HARDFLOAT") needs to be addressed. Unfortunately, 6.1 and
earlier do not contain commit e441273 ("Documentation: raise
minimum supported version of binutils to 2.25"), so it cannot be assumed
that all supported versions of GNU as have support for -msoft-float.

In order to switch from KBUILD_CFLAGS to KBUILD_AFLAGS in as-option
without consequence, move the '-Wa,-msoft-float' check to cc-option,
including '$(cflags-y)' directly to avoid the issue mentioned in
commit 80a20d2 ("MIPS: Always use -Wa,-msoft-float and eliminate
GAS_HAS_SET_HARDFLOAT").

Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/mips/Makefile

@@ -109,7 +109,7 @@ endif
 # (specifically newer than 2.24.51.20140728) we then also need to explicitly
 # set ".set hardfloat" in all files which manipulate floating point registers.
 #
-ifneq ($(call as-option,-Wa$(comma)-msoft-float,),)
+ifneq ($(call cc-option,$(cflags-y) -Wa$(comma)-msoft-float,),)
 	cflags-y		+= -DGAS_HAS_SET_HARDFLOAT -Wa,-msoft-float
 endif