msm: mdss: enable pll regulator during phy on sequence

Make sure pll regulator is enabled as part of the phy
on sequence. This fixes some corruption observed
when pll is disabled as part of the phy shut-down
sequence.

Change-Id: I1ace97dbf5b8e5ed8fceedddf714758a5f708cfb
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>