Add BOARD_GENFS_LABELS_VERSION

If it's 202504 or later, /sys/class/udc will be labeled as sysfs_udc. If
it's not set, /sys/class/udc will stay at the label sysfs. This is to
support GRF vendors older than 202504.

202404 or old vendors can choose either way. If they want to customize
permissions to /sys/class/udc, they can turn off
BOARD_GENFS_LABELS_VERSION and assign their own label to /sys/class/udc
/sys/class/udc with vendor sepolicy.

202504 or newer vendors must set BOARD_GENFS_LABELS_VERSION to a version
greater than or equal to 202504.

For now there's only one node /sys/class/udc, but more labels can be
added until 202504 freeze.

Bug: 361985697
Test: boot with and without BOARD_GENFS_LABELS_VERSION
Change-Id: I1a28109119368f1475628be85dd8d990c824922e