msm: gdsc: Collapse core memories during GDSC collapse on 8974

When a core is power-collapsed the contents of its internal
memories need not be retained. Collapse the memories to
save some additional power.

Change-Id: I1f9fd9a54017d24069d007b531b0a9706415a8b5
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>