TTY: simserial, fix includes

Use headers from linux/* instead of asm/. Remove declaration of
console_drivers, it's in linux/console.h already.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>