armv7: cache maintenance operations for armv7

- Add a framework for layered cache maintenance
	- separate out SOC specific outer cache maintenance from
	  maintenance of caches known to CPU

- Add generic ARMv7 cache maintenance operations that affect all
  caches known to ARMv7 CPUs. For instance in Cortex-A8 these
  opertions will affect both L1 and L2 caches. In Cortex-A9
  these will affect only L1 cache

- D-cache operations supported:
	- Invalidate entire D-cache
	- Invalidate D-cache range
	- Flush(clean & invalidate) entire D-cache
	- Flush D-cache range
- I-cache operations supported:
	- Invalidate entire I-cache

- Add maintenance functions for TLB, branch predictor array etc.

- Enable -march=armv7-a so that armv7 assembly instructions can be
  used

Signed-off-by: Aneesh V <aneesh@ti.com>