arm64: Add an initial GICv5 ITS driver

[andrew]

Summary

Add a driver to support the GICv5 interrupt translation service (ITS).
The ITS is responsible to handling ITS events & translating them to an
interrupt to be delivered to the interrupt routing service (IRS).

An example event is a MSI or MSI-X is delivered. The ITS will generate
an LPI depending on which device sent the interrupt and the value the
device wrote.

This is a similar concept to the GICv3 ITS, however the implementation
details are different so it needs a new driver.

Sponsored by: Arm Ltd

[andrew]

• Clean up table size/alignment handling
• Read the table PA range from the register
• Support 2 level device tables
• Support a non-coherent ITS
• Cleanup better on attach failure
• Implement more functions