FROMLIST: virt: gunyah: guestmem: Initialize RM mem parcels from guestmem

Gunyah Resource Manager sets up a virtual machine based on a device
tree which lives in guest memory. Resource manager requires this memory
to be provided as a memory parcel for it to read and manipulate.
Implement a function to construct a memory parcel from a guestmem
binding.

Bug: 338347082
Link: https://lore.kernel.org/all/20240222-gunyah-v17-25-1e9da6763d38@quicinc.com/


Change-Id: I2921381a5c066181bcaacbde4bae672837cb5e33
Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>