Fixes for 64bit in libhwui

Using reinterpret_cast allows conversions between pointer types
and integers which don't have the same size. The corresponding
flags is -Wint-to-pointer-cast.

Change-Id: I8ff0c79d235fa6d07b8d9305edc185d946d5133d
Signed-off-by: Kévin PETIT <kevin.petit@arm.com>