[media] bt8xx: Use current logging styles

This converts some messages that were emitted at
KERN_INFO to KERN_DEBUG.  All of these messages
were guarded by bttv_debug tests.

Add pr_fmt.
Convert printks to pr_<level>
Convert printks without KERN_<level> to appropriate pr_<level>.
Removed embedded prefixes when pr_fmt was added.
Whitespace cleanups when around other conversions.
Macros coded with if statements should be do { if... } while (0)
so the macros can be used in other if tests.
Use ##__VA_ARGS__ for variadic macro as well.
Coalesce format strings.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>