ACPI: NUMA: Establish a new drivers/acpi/numa/ directory

Currently hmat.c lives under an "hmat" directory which does not enhance
the description of the file. The initial motivation for giving hmat.c
its own directory was to delineate it as mm functionality in contrast to
ACPI device driver functionality.

As ACPI continues to play an increasing role in conveying
memory location and performance topology information to the OS take the
opportunity to co-locate these NUMA relevant tables in a combined
directory.

numa.c is renamed to srat.c and moved to drivers/acpi/numa/ along with
hmat.c.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>