ahci-remap.h: add ahci remapping definitions

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
[hch: split into a separate header and commit]
Signed-off-by: Christoph Hellwig <hch@lst.de>
[tj: dropped duplicate definition of AHCI_VSCAP spotted by Sergei]
Cc: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Tejun Heo <tj@kernel.org>