ACPI, APEI: Add RAM mapping support to ACPI

This patch adds support for RAM to ACPI's mapping capabilities in order
to support APEI error injection (EINJ) actions.

This patch re-factors similar functionality introduced in commit
76da3fb3

, bringing it into osl.c in preparation for removing
./drivers/acpi/atomicio.[ch].

Signed-off-by: Myron Stowe <myron.stowe@redhat.com>
Signed-off-by: Len Brown <len.brown@intel.com>