Add x86 and generic implementations of atomic_test_and_set_bit() to allow
KVM selftests to atomically manage bitmaps.

Note, the generic version is taken from arch_test_and_set_bit() as of
commit 415d8324 ("locking/atomic: Make test_and_*_bit() ordered on
failure").
Signed-off-by: Peter Gonda <pgonda@google.com>
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20221006003409.649993-5-seanjc@google.com