ALSA: radio/sound/miro: fix build, cleanup depends/selects

miropcm20 uses ALSA (snd_) interfaces from the SND_MIRO
driver, so it should depend on SND.
(selecting SND_MIRO when CONFIG_SND is not enabled is a
problem.)

drivers/built-in.o: In function `vidioc_s_ctrl':
radio-miropcm20.c:(.text+0x227499): undefined reference to `snd_aci_cmd'
drivers/built-in.o: In function `vidioc_s_frequency':
radio-miropcm20.c:(.text+0x227574): undefined reference to `snd_aci_cmd'
radio-miropcm20.c:(.text+0x227588): undefined reference to `snd_aci_cmd'
drivers/built-in.o: In function `pcm20_init':
radio-miropcm20.c:(.init.text+0x2a784): undefined reference to `snd_aci_get_aci'

miropcm20 selects SND_MIRO but SND_ISA may be not enabled, so
also select SND_ISA so that the snd-miro driver will be built.
Otherwise there are missing symbols:

ERROR: "snd_opl4_create" [sound/isa/opti9xx/snd-miro.ko] undefined!
ERROR: "snd_wss_pcm" [sound/isa/opti9xx/snd-miro.ko] undefined!
ERROR: "snd_wss_timer" [sound/isa/opti9xx/snd-miro.ko] undefined!
ERROR: "snd_wss_create" [sound/isa/opti9xx/snd-miro.ko] undefined!
ERROR: "snd_wss_mixer" [sound/isa/opti9xx/snd-miro.ko] undefined!

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Acked-by: Mauro Carvalho Chehab <mchehab@infradead.org>
Cc: Krzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: Takashi Iwai <tiwai@suse.de>