arm64: KVM: Move VCPU_WORKAROUND_2_FLAG macros to the top of the file

This is to avoid potential merging conflicts between commit 55e3748e
("arm64: KVM: Add ARCH_WORKAROUND_2 support for guests") and the KVM
tree.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>