msm: Rename pmem variables and macros

Since MSM no longer uses PMEM, the variables, macros, and kernel
config (CONFIG_KERNEL_PMEM_EBI_REGION) relating to PMEM should be
renamed to something more generic.

Change-Id: I4ca909098c96317853d4f040850b63f37db4811e
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>