ANDROID: KVM: arm64: Move PTE attributes definitions to the common header

Make PTE attribute definitions available from kvm_pgtable.h and take
them out of the pagetable code. These attributes will be used later in
mem_protect.c to construct different masks during the PTE manipulation
callbacks.

Bug: 222044487
Signed-off-by: Sebastian Ene <sebastianene@google.com>
Change-Id: I2f7108815ef0fa536e7f3314762a412119400fe9