UPSTREAM: common: Introduce processor.h

The vDSO library should only include the necessary headers required for
a userspace library (UAPI and a minimal set of kernel headers). To make
this possible it is necessary to isolate from the kernel headers the
common parts that are strictly necessary to build the library.

Introduce processor.h to contain all the processor specific functions
that are suitable for vDSO inclusion.

Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200320145351.32292-16-vincenzo.frascino@arm.com


(cherry picked from commit d8bb6993d871f5d3cd6d65d3772e4b1f4ef17380)
Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Bug: 154668398
Change-Id: Ibb70f49f4a711f4549d5a5efe8009b1903b144f3