Fishfooding: linux-firmware: add a build flag for RTL8822C

This change updates LINUX_FIRMWARE (which expends into a USE flag)
in order to pick the correct Bluetooth firmware file on RTL8822C.

Once the CL in the ToT is merged, this one should be reverted then
re-apply the formal merged one in the ToT.

BUG=b:139078086
TEST=Manually run with and without the chages (and depedencies), and
verify that the FW was loaded correctly.
Original-Cq-Depend: chromium:1692343
Original-Change-Id: I8d86b308f54b1bb6adc72a3571d14729cb09e229

Change-Id: I9d63673b4bc043dc14f3553b86139a367ccb5efa
1 file changed