mmc: msm_sdcc: enable asynchronous interrupt support in 4-bit mode

SDIO 3.0 specification has added the support for asynchronous interrupt
period during which card allows the clock to be gated off.

As SDCC driver is capable of handling the asynchronous interrupt, advertise
MMC_CAP2_ASYNC_SDIO_IRQ_4BIT_MODE capability.

CRs-Fixed: 490008
Change-Id: Ic292f379795a821a0aa678d439eac9c2e3e560b7
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>