kselftest/alsa: pcm - Provide descriptions for the default tests

Help people understand what the standard tests are trying to cover by
providing descriptions which both serve as comments in the file and log
messages in the program's output.

Reviewed-by: Jaroslav Kysela <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Takashi Iwai <[e-mail]>

tools/testing/selftests/alsa/pcm-test.conf

···
 pcm.test.time1 {
+	description "48kHz stereo small periods"
 	format S16_LE
 	alt_formats [ S32_LE ]
 	rate 48000
···
 	buffer_size 4096
 }
 pcm.test.time2 {
+	description "48kHz stereo large periods"
 	format S16_LE
 	alt_formats [ S32_LE ]
 	rate 48000