mmc: core: export mmc_host_may_gate_card function

MMC Host driver might want to use the mmc_host_may_gate_card() API
to know whether the clock can be gated to the card or not hence
export this function for usage outside its current scope.

Change-Id: Idb1e6a7da15cf638b365af952ea8860b1e89c5ba
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>
mmc: msm_sdcc: fix clock gating handling using pwrsave control bit

SDCC controller provides the PWRSAVE control bit to automatically
disable the clock to card when there is no activity with card. SDCC
host controller driver always enables this feature but few SDIO
cards may require the clocks to be always running (even during
inactivity period) to raise the interrupt notification to host so
for such cards, enabling PWRSAVE fature may cause functional failures.

This change checks whether it is ok to gate the card clock before
enabling the PWRSAVE feature.

Change-Id: I52915dbd015de496494dbf8bd5e202cfa869ebaf
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>