[ARM] Make -mcpu, -march and -mtune case-insensitive

gcc/

	* config/arm/arm.opt: Make -mcpu, -march, -mtune case-insensitive.



git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@206673 138bc75d-0d04-0410-961f-82ee72b054a4