ANDROID: KVM: arm64: Convert pKVM 'vm_table_lock' to an rwlock

Convert 'vm_table_lock' from a spinlock to an rwlock so that walks of
the table are not serialising, allowing different 'hyp_vcpu' structures
to be loaded concurrently.

The conversion is mostly straighforward, although a cmpxchg() is needed
to ensure that the same 'hyp_vcpu' cannot be loaded on two physical CPUs
simultaneously.

Cc: Fuad Tabba <tabba@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
Bug: 278749606
Change-Id: Iea2f61f26afd535837c0923d4320b2beeab01109