soc: qcom: pil: Allow the MBA memory to be dynamic or a carveout

Currently, the MBA is expected to be loadable at any
region in DDR. However, due to limitations in the modem
PBL or MBA image, this is not always possible. Allow
the modem to be loaded in a carved out CMA heap if specified
in device tree. Current memory APIs do not allow the association
of more than one memory region with a device; therefore
allow the existence of an optional sub-device node that
will contain the memory region property for the MBA.

CRs-Fixed: 2006100
Change-Id: Ia2b52be55f0b3f23278e1f71106fdb46de1d0fe1
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>
Signed-off-by: Puja Gupta <pujag@codeaurora.org>