printk/console: Split out code that enables default console

Put the code enabling a console by default into a separate function
called try_enable_default_console().

Rename try_enable_new_console() to try_enable_preferred_console() to
make the purpose of the different variants more clear.

It is a code refactoring without any functional change.

Signed-off-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Link: https://lore.kernel.org/r/20211122132649.12737-2-pmladek@suse.com