Support AWS graviton

[wkozaczuk]

Make OSv runnable on AWS graviton-based EC2 instances - see https://aws.amazon.com/ec2/graviton/.

This depends on the following issues:

• support ENA (see Implement AWS ENA driver #1204) - completed
• support GICv3 (see Implement GICv3 #1290) - completed
• support MSI/X (see Missing MSI-X support in the AArch64 port #1088)
• support ACPICA on aarch64 (see Add acpica support to aarch64 #1294)
• support UEFI boot (see UEFI support #1098)