fs/common.mk: rename FULL_DEVICE_TABLE to ROOTFS_FULL_DEVICES_TABLE

fs/common.mk: rename FULL_DEVICE_TABLE to ROOTFS_FULL_DEVICES_TABLE

In commit 6b50f988ad0a6044530b30344d52139da2994237 ("fs/common.mk:
rename internal variable"), USERS_TABLE was renamed to
ROOTFS_FULL_USERS_TABLE.

This commit follows the same direction by renaming the
FULL_DEVICE_TABLE variable to ROOTFS_FULL_DEVICE_TABLE.

In addition, for consistency, the file itself is renamed
full_device_table.txt.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>