Since 9a46ad6d ("smp: make smp_call_function_many() use logic
similar to smp_call_function_single()"), the core IPI handling
has been simplified, and generic_smp_call_function_interrupt is
now the same as generic_smp_call_function_single_interrupt.

This means that one of IPI_CALL_FUNC and IPI_CALL_FUNC_SINGLE has
become redundant. We can then safely drop IPI_CALL_FUNC_SINGLE,
and use only IPI_CALL_FUNC.

This has the advantage of reducing the number of SGI IDs we're using
(a fairly scarse resource).

Tested on a dual A7 board.
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>