MIPS: BCM63xx: Replace irq dispatch code with a generic version

MIPS: BCM63xx: Replace irq dispatch code with a generic version

The generic version uses a variable length of u32 registers instead of u32/u64.
This allows easier support for "wider" registers without having to rewrite
everything.

This "generic" version is as fast as the old version in the best case
(i == next set bit), and twice as fast in the worst case in 64 bits.

Using a macro was chosen over a (forced) inline version because gcc generated
more compact code with the macro.

The change from (signed) int to unsigned int for i and to_call was intentional
as the value can be only between 0 and (width - 1) anyway, and allowed gcc to
optimise the code a bit further.

Signed-off-by: Jonas Gorski <jogo@openwrt.org>
Cc: linux-mips@linux-mips.org
Cc: John Crispin <blogic@openwrt.org>
Cc: Maxime Bizon <mbizon@freebox.fr>
Cc: Florian Fainelli <florian@openwrt.org>
Cc: Kevin Cernekee <cernekee@gmail.com>
Cc: Gregory Fong <gregory.0xf0@gmail.com>
Patchwork: https://patchwork.linux-mips.org/patch/7316/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>