Add an option to move 16K ota to vendor partition

For GRF devices, the system partition might be shared between different
products using different kernels. Hence putting the 16K boot option OTA
on system partition would not work for such project.

Test: th
Bug: 293313353
Bug: 328166454
Bug: 329808458

Change-Id: I2ba3ad4f28f3569c6b8e275849988328f9d73552