Add a prefixing macro to dev_<level> uses similar to the pr_fmt
prefixing macro used in pr_<level> calls.

This can help avoid some string duplication in dev_<level> uses.

The default, like pr_fmt, is an empty #define dev_fmt(fmt) fmt

Rename the existing dev_<level> functions to _dev_<level> and
introduce #define dev_<level> _dev_<level> macros that use the
new #define dev_fmt

Miscellanea:

o Consistently use #defines with fmt, ... and ##__VA_ARGS__
o Remove unnecessary externs
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>