Compile libhwui.so with 2MB section alignment.

Adds the appropriate linker flags for libhwui to have 2MB section
alignment. This allows the executable segments of the library to be
backed by transparent hugepages on supporting systems.

Bug: 158135888
Test: Verified ELF format
Change-Id: I232ac4a8b753384bd92429b21ca703b74aa15ac9