tune-cortexa.inc: create a common include for cortex-a armv7a tuning

tune-cortexa.inc: create a common include for cortex-a armv7a tuning

The tuning files for the cortex-a* processors are mostly identical for
the A7,A8,A9,A15 processors. Rework these files to use a CORTEX_ID
variable to setup the tuning for each specific processor.

(From OE-Core rev: 3e4f4a1cf07ff7cf4c71566492385f8fbf581789)

Signed-off-by: Andy Voltz <andy.voltz@timesys.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>