arm/dt: msmcopper: Change LDO13 constraints to support 1.8V

LDO13 powering VDDPX_2 (SD card I/O) pad supports switching
between 1.8V and 2.95V. Hence, change the constraints to
accomodate 1.8V.

Change-Id: Ib4569273e7b75cb9964b4c9e865dbc1c1e6fdd46
Signed-off-by: Sujit Reddy Thumma <sthumma@codeaurora.org>