ARM: SMP: remove IRQ-disabling for smp_cross_call()

As we've now removed the spinlock and bitmask, we have nothing left
which requires interrupts to be disabled when sending an IPI.  All
current IPI-sending implementations use the GIC, which also does not
require interrupts disabled when calling gic_raise_softirq().

Remove the now unnecessary IRQ disable.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>