linux: scm: Update the API for assign memory to subsys

Update the API of the mdf assign memory to subsys for cases
when the scm driver is not compiled. The current API has an
extra parameter.

Change-Id: I50c100d2ee260a14fe754a8497727b5d37d20610
Signed-off-by: Siddharth Gupta <sidgup@codeaurora.org>