PCI/MSI: Rename msi_desc::masked

msi_desc::masked is a misnomer. For MSI it's used to cache the MSI mask
bits when the device supports per vector masking. For MSI-X it's used to
cache the content of the vector control word which contains the mask bit
for the vector.

Replace it with a union of msi_mask and msix_ctrl to make the purpose clear
and fix up the usage sites.

No functional change

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210729222543.045993608@linutronix.de