Allow to override fastboot-info.txt for specific board

Introduce TARGET_BOARD_FASTBOOT_INFO_FILE to override
fastboot-info.txt generated by default

Test: locally with CF target on related change
Bug: 315811289
Change-Id: I52208e49ac1dfe8558849be9befa60df805665e3
Signed-off-by: Dmitrii Merkurev <dimorinny@google.com>