ASoC: SOF: core: Skip firmware test for custom loaders

ASoC: SOF: core: Skip firmware test for custom loaders

The ACP driver for Vangogh platform uses a quirk for Valve Galileo
device to setup a custom firmware loader, which neither requires nor
uses the firmware file indicated via the default_fw_filename member of
struct sof_dev_desc.

Since commit 6c393ebbd74a ("ASoC: SOF: core: Implement IPC version
fallback if firmware files are missing"), the provided filename gets
verified and triggers a fatal error on probe:

[ 7.719337] snd_sof_amd_vangogh 0000:04:00.5: enabling device (0000 -> 0002)
[ 7.721486] snd_sof_amd_vangogh 0000:04:00.5: SOF firmware and/or topology file not found.
[ 7.721565] snd_sof_amd_vangogh 0000:04:00.5: Supported default profiles
[ 7.721569] snd_sof_amd_vangogh 0000:04:00.5: - ipc type 0 (Requested):
[ 7.721573] snd_sof_amd_vangogh 0000:04:00.5:  Firmware file: amd/sof/sof-vangogh.ri
[ 7.721577] snd_sof_amd_vangogh 0000:04:00.5:  Topology file: amd/sof-tplg/sof-vangogh-nau8821-max.tplg
[ 7.721582] snd_sof_amd_vangogh 0000:04:00.5: Check if you have 'sof-firmware' package installed.
[ 7.721585] snd_sof_amd_vangogh 0000:04:00.5: Optionally it can be manually downloaded from:
[ 7.721589] snd_sof_amd_vangogh 0000:04:00.5:    https://github.com/thesofproject/sof-bin/
[ 7.721997] snd_sof_amd_vangogh: probe of 0000:04:00.5 failed with error -2

According to AMD, a combined ".ri" file which includes the code and data
segments cannot be used due to a limitation preventing the code image to
be signed on build time.

Fix the issue by skipping the firmware file test if a custom loader is
being used instead of the generic one.

Fixes: 6c393ebbd74a ("ASoC: SOF: core: Implement IPC version fallback if firmware files are missing")
Co-developed-by: Péter Ujfalusi <peter.ujfalusi@linux.intel.com>
Signed-off-by: Péter Ujfalusi <peter.ujfalusi@linux.intel.com>
Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Link: https://msgid.link/r/20231219030728.2431640-8-cristian.ciocaltea@collabora.com
Signed-off-by: Mark Brown <broonie@kernel.org>