USB: phy-msm: Enable core/async irq only for host/device bus suspend

Currently driver is enabling both USB core irq and async irq as part of
entering low power mode during cable disconnect. These irqs are not
required to enable during low power mode in case of cable disconnect as
USB depends on PMIC hardware for detection of cable connect/disconnect
and host mode. Hence disable those irqs as part of low power mode and
enable them only for host bus suspend and device bus suspend scenarios.

Change-Id: Id0f3f97b360c1d6adee9d6a0fd2eff1961147ea0
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>