x86/svm: Improve code generation from cpu_has_svm_feature()

x86/svm: Improve code generation from cpu_has_svm_feature()

Taking svm_feature_flags by pointer and using test_bit() results in generated
code which loads svm_feature_flags into a 32bit register, then does a bitwise
operation.

The logic can be expressed in terms of a straight bitwise operation, resulting
in the following minor improvement.

  add/remove: 0/0 grow/shrink: 0/4 up/down: 0/-136 (-136)
  Function                                     old     new   delta
  svm_nested_features_on_efer_update           281     273      -8
  svm_create_vmcb                             1404    1388     -16
  svm_vmexit_handler                          6271    6239     -32
  start_svm                                    818     738     -80
  Total: Before=3347569, After=3347433, chg -0.00%

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>