Add NDK methods for HARDWARE Bitmaps

Bug: 135133301
Test: I2c1e58c41e49c72fb4bdbc64989da103885d34bf

Add a flag for AndroidBitmapInfo.flags that represents whether the
Bitmap has Config.HARDWARE.

Add a method for retrieving the AHardwareBuffer if it is a HARDWARE
Bitmap.

Change-Id: I69b78491bc29e770d863aa01752e8c923298afb3