ASoC: soc-core: disable route checks for legacy devices

v5.4 changes in soc-core tightened the checks on soc_dapm_add_routes,
which results in the ASoC card probe failing.

Introduce a flag to be set in machine drivers to prevent the probe
from stopping in case of incomplete topologies or missing routes. This
flag is for backwards compatibility only and shall not be used for
newer machine drivers.

Example with an HDaudio card with a bad topology:

[ 236.177898] skl_hda_dsp_generic skl_hda_dsp_generic: ASoC: Failed to
add route iDisp1_out -> direct -> iDisp1 Tx

[ 236.177902] skl_hda_dsp_generic skl_hda_dsp_generic:
snd_soc_bind_card: snd_soc_dapm_add_routes failed: -19

with the disable_route_checks set:

[ 64.031657] skl_hda_dsp_generic skl_hda_dsp_generic: ASoC: Failed to
add route iDisp1_out -> direct -> iDisp1 Tx

[ 64.031661] skl_hda_dsp_generic skl_hda_dsp_generic:
snd_soc_bind_card: disable_route_checks set, ignoring errors on
add_routes

Fixes: daa480bd

 ("ASoC: soc-core: tidyup for snd_soc_dapm_add_routes()")
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Acked-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/20200309192744.18380-2-pierre-louis.bossart@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>