PCI MSI: Remove unused/obsolete macros and definitions

Impact: cleanup, spec compliance

This patch does:

 - Remove unused msi/msix_enable/disable macros.
   User should use msi/msix_set_enable() functions instead.

 - Remove unused msix_mask/unmask/pending macros.
   These macros are useless because they are not based on any of
   the PCI Local Bus Specifications properly.
   It seems that they were written based on a draft of PCI spec,
   and that the draft was the MSI-X ECN that underwent membership
   review in September 2002.
   (* In the draft, the size of a entry in MSI-X table was 64bit,
      containing 32bit message data and DWORD aligned lower address
      plus a pending bit and a mask bit.(30+1+1bit)  The higher
      address was placed in MSI-X capability structure and shared
      by all entries.)

 - Remove PCI_MSIX_FLAGS_BITMASK.
   This definition also come from the draft ECN.

Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Reviewed-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>