arm: use -mcpu=cortex-a9 when targeting u8500 cpus (cortex-a9 based), this is done in order to force compliant GCC compiler to generate the new
sdiv/udiv instructions supported by Cortex-A9 architecture

Change-Id: I8ab361ef6d76b4e4d02e11b036d91535bb86b15b
Signed-off-by: zwliew <zhaoweiliew@gmail.com>