[PATCH] Update compilation flags with core specific options

[Udma Catalin-Dan-B32721]

> This breaks the vdso for e500v1/v2 (userspace dies with SIGILL), since
> KBUILD_CFLAGS doesn't get used when building asm files, and the vdso
> uses mftbu/mftbl which are not being assembled to the form that
> e500v1/v2 support.
> 
> We should be setting -mcpu=whatever and -msoft-float in both CFLAGS and
> AFLAGS, since we don't call "as" directly, and target selection should
> not differ based on whether we're building a C file or an asm file.
> 
> -Scott
[CU] Thank you, Scott. I'll update also AFLAGS.

I have some questions about how you reproduce the SIGILL issue.
I tried to reproduce the issue looking to gettimeofday.S, that uses
mftbu/mftbl. In my tests, I obtained the same output when compiling this file
for p1021rdb before and after this patch, and also after adding -mcpu to
AFLAGS: "objdump -d arch/powerpc/kernel/vdso32/gettimeofday.o" looks the same
for the cases mentioned above:
   "mftbu r3" from .S file is decoded to "mfspr   r3,269" in "objdump -d" output

Indeed, for -mcpu=601/power3, the "objdump -d" output is "mftbu r3" and according to
powerISA this instruction would cause Illegal Instruction error handler to be invoked
and permits the sw to emulate the instruction.

Regards,
Catalin