disp: msm: sde: remove dspp blocking

RM blocks an lm path with dspp from being allocated if a dspp is
not required by topology. This can restrict using all lms to full
availability. LM preference already ensures dspp
assignment is completed to required built in displays.
This change removes blocking conditions.

Change-Id: Ifec6f27d4d10a9ea061780ed5f9e9601b893d5a0
Signed-off-by: Nilaan Gunabalachandran <ngunabal@codeaurora.org>