PCI: aardvark: Add support for masking MSI interrupts

We should not unmask MSIs at setup, but only when kernel asks for them
to be unmasked.

At setup, mask all MSIs, and implement IRQ chip callbacks for masking
and unmasking particular MSIs.

Link: https://lore.kernel.org/r/20220110015018.26359-11-kabel@kernel.org
Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Marek Behún <kabel@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>