gsm-fw/L1: fix for the DSP patch corruption bug The L1 code we got from the LoCosto fw contains a feature for DSP CPU load measurement. This feature is a LoCosto-ism, i.e., not applicable to earlier DBB chips (Calypso) with their respective earlier DSP ROMs. Most of the code dealing with that feature is conditionalized as #if (DSP >= 38), but one spot was missed, and the MCU code was writing into an API word dealing with this feature. In TCS211 this DSP API word happens to be used by the DSP code patch, hence that write was corrupting the patched DSP code.

L1S (l1_cmplx.c specifically) calls these 3 functions which are normally
defined in the DL protocol stack entity:

dll_dcch_downlink()
dll_read_dcch()
dll_read_sacch()

If we are building L1 standalone (without the G23 protocol stack), we need
to provide stubs for these functions.