Surface: Fix gralloc flags conflicting values.

Due to some custom code, unwanted flags (HW) got added with SW flags.
Restrict the flags to custom ones.

Change-Id: I2ab1c75eef4d6d16f0dd7d43aff3c7377486801a
libgui: Fix building with QCOM_BSP + CAF display

Change-Id: Iaf0eb69fa7f409144a266ada683fceb835f62aff