msm: pil: Use platform_get_resource_byname() on device-tree targets

Using indexes with platform_get_resource() is error-prone when
the array being indexed is long. Use string names when getting
register bases from device tree instead.

Change-Id: I6543b0f2819f2325719bf1508594a2cb34a548cf
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>