irqchip/gic-v3: Relax polling of GIC{R,D}_CTLR.RWP

Recent work on the KVM GIC emulation has revealed that the GICv3
driver is a bit RWP-happy, as it polls this bit for each and
every write MMIO access involving a single interrupt.

As it turns out, polling RWP is only required when:
- Disabling an SGI, PPI or SPI
- Disabling LPIs at the redistributor level
- Disabling groups
- Enabling ARE
- Dealing with DPG*

Simplify the driver by removing all the other instances of RWP
polling, and add the one that was missing when enabling the distributor
(as that's where we set ARE).

Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220405183857.205960-4-maz@kernel.org