layer1/l1ctl: Split L1CTL_NEW_CCCH_REQ in FBSB_REQ nad SYNC_REQ

layer1/l1ctl: Split L1CTL_NEW_CCCH_REQ in FBSB_REQ nad SYNC_REQ

We really want to have those two as distinct operations - and we
want proper state machines in L1 to quickly return if they've
managed to acquire a FB or SB or not.  Otherwise scanning will
take ages...

This code now introduces a new l1ctl_fbsb_req that is sent via
L1CTL to ask for a bitmask of FB0/FB1/SB operations.  The actual
FB0/FB1 detection now no longer runs for 500 TDMA interrupts
but completes as soon as we either know there is no FCCH,
or that our frequency error is smaller than a caller-specified
threshold.

FB0/FB1 are already working, SB is not yet, sorry.