AArch64: Use long for pointers in SurfaceTexture

Long is used in SurfaceTexture class to store
pointers as native pointers can be 64-bit.

In addition, some minor changes have been done
to conform with standard JNI practice (e.g. use
of jint instead of int in JNI function prototypes)

Change-Id: I771aa62c42bc865e644c63fd48f309782dd03e73
Signed-off-by: Ashok Bhat <ashok.bhat@arm.com>
Signed-off-by: Kévin PETIT <kevin.petit@arm.com>