Add -O2 option to AFLAGS to enable asm code optimization for m32r.

On m32r gas, "-m32r2 -O" option enables assembler's parallel code
generation optimization for M32R2 ISA as a default.  So, "-no-parallel"
option is required explicitly for a cpu core with single instuction
issuing, for example, VDEC2.
Signed-off-by: Hirokazu Takata <takata@linux-m32r.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>