ANDROID: vendor hooks: Export symbols for bootloader based hibernation

To add encryption support to bootloader based hibernation, export
symbols snapshot_get_image_size and alloc_swapdev_block.

These symbols can be used by vendor implementation to be called before
and after storing the snapshot image.

Bug: 260069271
Change-Id: I0d44bf833a97fce5bc5213712b2b2523a9e22607
Signed-off-by: Shreyas K K <quic_shrekk@quicinc.com>