ARM: dts: msm: enable HS400 for msm8994

MSM8994 supports HS400 for eMMC and hence updating the device node
information to reflect that support.

Right now only the mtp platforms are stable for HS400 mode. Fix the
eMMC clock line drive strength to an appropriate value for mtp
platforms.

After the issues with cdp platforms are resolved, then HS400 mode
for those platforms will be enabled.

Change-Id: I256b905a25624bf13203d359b2fa7ac29f58d945
Signed-off-by: Krishna Konda <kkonda@codeaurora.org>