[media] media: tea5764: reconcile Kconfig symbol and macro

The Kconfig symbol RADIO_TEA5764_XTAL is unused. The code does use a
RADIO_TEA5764_XTAL macro, but does that rather peculiar. But there seems
to be a way to keep both. (The easiest way out would be to rip out both
the Kconfig symbol and the macro.)

Note there's also a module parameter 'use_xtal' to influence all this.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>