feat(cpufeat): add memory retention bit define for CLUSTERPWRDN

Bit1 in the CLUSTERPWRDN register is used to indicate on CLUSTERPACTIVE
that memory retention is required or not. It can be used for
L3 cache memory retention support.

Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Change-Id: I1c53c90ae3dfbed3be7e5b2b79f2c3565db81012
2 files changed