mmc: sdhci-msm: 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.

Change-Id: Id5a86bc70b7b798b23be3a0fc0d59b2db05e0409
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>