dt-bindings: ufs: Supply vccq/vccq2 regulator min load for LPM mode

To configure regulator in LPM mode, on some targets explicit load
(<10mA or <30mA) has to be supplied. On other targets, clients need to
set load exactly as 0. On second category of targets, any load value
other than 0, pushes the regulator to NMP mode.

Adding support for supplying load value for Vccq/Vccq2 regulator from
device tree, so that different loads can be supplied for different
targets.

Change-Id: I902673c1080612632df30f80c8c2a138a00d4c1e