msm: mdss: Check valid PP hardware configs based on mfd

The logic for validating the hardware configuration of the mixers, AD
hardware, and DSPPs in a display pipeline has been simplified. If an
incoming PP configuration is invalid and PP hardware is not available,
a warning is printed. Invalid configurations are recoverable, however.

Change-Id: Ib3a6206a8c181390fb6ee5a6761e5ea857b37e1a
Signed-off-by: Benet Clark <benetc@codeaurora.org>