ARM: 7536/1: smp: Formalize an IPI for wakeup

Remove the offset from ipi_msg_type and assume that SGI0 is the
wakeup interrupt now that all WFI hotplug users call
gic_raise_softirq() with 0 instead of 1. This allows us to
track how many wakeup interrupts are sent and also removes the
unknown IPI printk message for WFI hotplug based systems.

Reviewed-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>