msm: mdss: fix wb format enumeration

Enumeration for writeback is not properly done because not all
information from device tree has been retrieved before setting up
supported formats. Moved this call until all data has been retrieved
from device tree and hw pre initialization.

Change-Id: Id228bf7ec564669fa8e9e739e27052de0133cc4d
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>