arm/dt: msm8974: set emmc regulator to always on

With current hardware if emmc regulator is turned off, the regulator
is not reset and turned on if a msm reset is issued via jtag. So in
order to work around this issue, that regulator is marked as always
on and low power mode support is enabled.

Change-Id: Idddceac95cb89719e7cfe2fa0751e79ec70dfa4b
Signed-off-by: Krishna Konda <kkonda@codeaurora.org>