msm: clock: Update memory retention clock flags

Introduce CLKFAG_{NO}RETAIN_PERIPH, which will eventually be used on
8974 to control collapse of the core memory periphery. To avoid
confusion with CLKFAG_{NO}RETAIN, rename those existing flag to
CLKFAG_{NO}RETAIN_MEM, to better indicate that they control retention
of the core's memory.

Change-Id: I078bcc7026095ab4b94dc57362220a5b05621bec
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>