drm/msm/sde: relax crtc for driving multiple connectors

Extend crtc implemtation for supporting a copy connector
by limiting roi checks and mixer info population for only
primary connector and remove existing bail out checks to
restrict crtc to single connector.

Change-Id: I6272d75625770e19b0fbb0427d262d349827390d
Signed-off-by: Prabhanjan Kandula <pkandula@codeaurora.org>