i8253: Move remaining content and delete asm/i8253.h

Move setup_pit_timer() declaration to the common header file and
remove the arch specific ones.

[ tglx: Move it to linux/i8253.h instead of asm/mips and asm/x86 ]

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: Russell King <linux@arm.linux.org.uk>
Cc: linux-mips@linux-mips.org
Cc: Sergei Shtylyov <sshtylyov@mvista.com
Link: http://lkml.kernel.org/r/20110601180610.913463093@duck.linux-mips.net
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>