gpu: ion: Check for release/request functions before calling
gpu: ion: Check for release/request functions before calling

Not all heaps will implement the release/request callbacks. Check those
function pointers are valid before calling.

Change-Id: I848e31495e45c7eaa4497b82be590d291d77980a
Signed-off-by: Laura Abbott <e7b4910f4742918f5926c991d8a2cd122ac7e295@codeaurora.org>

TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas