drm/msm: control regulator through s/w based on disp_rsc availability

Enable the regulator only for the first time through software
when the target is RSCC enabled. After that, RSCC hardware will
take care of toggling the regulator appropriately during suspend/
resume or idle pc cases. When display rsc is not available/enabled,
gdsc regulator is fully controlled through the software.

Change-Id: Icca05b8969d0f9589c00ab51fd790658b23f42d3
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>