qcom: sdm845: rename the modem firmware

The Qualcomm SDM845 platform has a modem-less version, called SDA845.
It still has the modem DSP, which is used for WiFi, GNSS, etc. The
firmware in the qcom/sdm845 dir comes from the Thundercomm RB3 board,
which internally has the SDA845 SoC rather than the full SDM845.

The SC8180X platform (not yet added to linux-firmware) started using
modem.mbn and modem_nm.mbn, the latter being used for no-modem
platforms.

Follow this example and rename qcom/sdm845/modem.mbn firmware
file to modem_nm.mbn. This commit adds a compatibility link for now, to
let the device trees to be adapted to this change. It should be removed
when the proper qcom/sdm845/modem.mbn is submitted.

Cc: Caleb Connolly <caleb.connolly@linaro.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

WHENCE

@@ -5646,8 +5646,9 @@ https://github.com/andersson/pil-squasher
 Driver: qcom_q6v5_mss - Qualcomm modem subsystem firmware
 
 File: qcom/sdm845/mba.mbn
-File: qcom/sdm845/modem.mbn
+File: qcom/sdm845/modem_nm.mbn
 File: qcom/sdm845/modemuw.jsn
+Link: qcom/sdm845/modem.mbn -> modem_nm.mbn
 
 Licence: Redistributable. See LICENSE.qcom and qcom/NOTICE.txt for details