ARM: Use -mcpu=cortex-a15 when targeting MSM Krait CPUs

Enable compiler optimizations specific to the Cortex-A15
processor when targeting MSM Krait CPUs. This is necessary
take advantage of the UDIV/SDIV instructions supported by
these processors. To accomplish this, we need to remove the
-march=armv7-a ISA restriction from the compiler options
because 'cortex-a15' is a superset of 'armv7-a'.

Signed-off-by: Stepan Moskovchenko <stepanm@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
arm: Add architecture details

Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
build: Sprinkle some Chaos!

Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>