build: Relax Cortex CFLAGS

 * Always set march=armv7-a
 * Use mtune instead of mcpu. Bad code is generated on A15 otherwise.

Change-Id: Idf8ced8eb0e9d3d4676ca8ec69bf56aed5533bf4
FDO: Only support locally

The issues:
  - The size increase from utilizing FDO is quite large while
    utilizing runtime profiles in build.
  - By default, FDO is utilized globally if the target arch variant
    profiles exist.
  - Not all modules can show statistical significance in
    performance comparison, yet still suffer the size increase.

The solution:
  - Only enable FDO locally with LOCAL_FDO_SUPPORT
    for modules which may benefit enough to justify the size
    tradeoff.

Solution notes:
  - I've noted statistical significance in libwebcore and libskia
    thus far from utilizing FDO.
  - Analysis included sunspider, drawcanvas benchmarks, as
    well as gooda analysis on both arm and x86
  - To support runtime profile generation in modules which have
    LOCAL_FDO_SUPPORT specified,
    BUILD_FDO_INSTRUMENTATION is still used. Otherwise,
    if the target arch variant profiles exist, FDO is utilized for
    specified modules.

Change-Id: I7e95266943ff47c7d82b02e6200fd09911d0bb57

Conflicts:
	core/binary.mk