msm: pil: remove use of MSM_IMEM_BASE

Move to getting address for PIL region of IMEM from the device tree and
mapping via ioremap.  This removes a usage of MSM_IMEM_BASE which will
allow removal of the static IO mappings.

Change-Id: I1321c978e4c102bfafcfb1a1c04464e31ae59943
Signed-off-by: Kumar Gala <galak@codeaurora.org>