irqchip/apple-aic: Add a new "Global fast IPIs only" feature level

irqchip/apple-aic: Add a new "Global fast IPIs only" feature level

Starting with the A11 (T8015) SoC, Apple began using arm64 sysregs for
fast IPIs. However, on A11, there is no such things as "Local" fast IPIs,
as the SYS_IMP_APL_IPI_RR_LOCAL_EL1 register does not seem to exist.

Add a new feature level, used by the compatible "apple,t8015-aic",
controlled by a static branch key named use_local_fast_ipi. When
use_fast_ipi is true and use_local_fast_ipi is false, fast IPIs are used
but all IPIs goes through the register SYS_IMP_APL_IPI_RR_GLOBAL_EL1, as
"global" IPIs.

Signed-off-by: Nick Chan <towinchenmi@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Sven Peter <sven@svenpeter.dev>
Link: https://lore.kernel.org/all/20240901034143.12731-4-towinchenmi@gmail.com