mmc: core: set MMC_PM_KEEP_POWER for certain Hynix mmc cards

Certain Hynix eMMC 5.0 cards might reach a fast EOL if
the card's power is disabled between CMD5 and CMD0
(power off during reset).
This patch sets the MMC_PM_KEEP_POWER flag to indicate
that the card's power should be retained for suspend/resume
sequences.

Change-Id: I4bcc0f4bfd608745626816ca261369b432602c45
Signed-off-by: Dov Levenglick <dovl@codeaurora.org>