msm: mdss: avoid shutting down PHY PMIC regulators

As part of the PHY shut down sequence, current driver
disable the phy pmic regulators. This is not the
expected sequence, so make sure the pmic phy
regulators stay enabled.

Change-Id: Ia65a71347666ed9fa3f6bf92fe7c573638301254
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>