Revert "Revert "libgui: Use fences for all QCOM targets""

This reverts commit 46c300879088bfd654c6be179fbd6bbacc519585.
ui: Allocate the custom buffer size in the failure case also

The custom buffer size was not being honored if memory allocation
failed in the first pass.
Also - removing an unnecessary check.

Change-Id: Ie501b2dda3843454405fec05fc898fec5912bd06
Don't use fence sync for qcom legacy

Change-Id: Ice64233a25edee763a36a3ba34230d1360a0d610