metag: smp: don't set irq regs in do_IPI()

Since commit f6b30d32d242 (metag: kick: add missing irq_enter/exit to
kick_handler()), the main kick_handler() function deals with setting and
restoring the irq registers pointer. Therefore do_IPI() which is called
indirectly from kick_handler() doesn't need to do that itself any
longer. Therefore remove that code and do_IPI()'s pt_regs argument.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: linux-metag@vger.kernel.org
Cc: Thomas Gleixner <tglx@linutronix.de>