firmware: cs_dsp: Factor out common debugfs string read

firmware: cs_dsp: Factor out common debugfs string read

cs_dsp_debugfs_wmfw_read() and cs_dsp_debugfs_bin_read() were identical
except for which struct member they printed. Move all this duplicated
code into a common function cs_dsp_debugfs_string_read().

The check for dsp->booted has been removed because this is redundant.
The two strings are set when the DSP is booted and cleared when the
DSP is powered-down.

Access to the string char * must be protected by the pwr_lock mutex. The
string is passed into cs_dsp_debugfs_string_read() as a pointer to the
char * so that the mutex lock can also be factored out into
cs_dsp_debugfs_string_read().

wmfw_file_name and bin_file_name members of struct cs_dsp have been
changed to const char *. It makes for a better API to pass a const
pointer into cs_dsp_debugfs_string_read().

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Link: https://patch.msgid.link/20251120130640.1169780-2-rf@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>