msm: mdss: Using target available DSPP numbers for validation in PP

In PP the validation for DSPP number is being done using macro
variable, whose value is constant across targets. Different targets
have different number of DSPP and validation is done based on
check for DSPP number exceeding the maximum available DSPPs on
target with highest DSPP available.

Using the number of mixers present information present in device
tree for validation. This provides validation specific to target.

There is a bug in freeing heap memory in PP terminate. The struct
mdss_pp_res is checked incorrectly in terminate before being
freed. Inverted the conditional check to perform rightful check.

Change-Id: I854dd59c93a8712e5b8b05ff27a7661117998777
Signed-off-by: Krishna Chaitanya Parimi <cparimi@codeaurora.org>
Signed-off-by: Carl Vanderlip <carlv@codeaurora.org>