MIPS: Kconfig: optimize gcc -march and -mtune setup

Move setup of -march to arch/mips/Makefile and follow the design on ARM.
Also add a possibility to chose specific CPU tune options.

Signed-off-by: Wills Wang <wills.wang@live.com>
Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
4 files changed