ANDROID: vendor_hooks: add hooks for extra memory

Add vendor hooks for extra memory. If there is extra memory, this can
be accounted like other memory stats. One of the usecases could be
cleancache. If some of ram memory is used for cleancache, its free,
cache, and total size could be added through these vendor hooks.

Bug: 283896254

Change-Id: Iad7330310528581f09842f45860f05dc84823f41
Signed-off-by: Jaewon Kim <jaewon31.kim@samsung.com>