sata_promise: mmio access cleanups

This patch cleans up sata_promise's mmio accesses.

In sata_promise there are three distinct mmio address spaces:
1. global registers, offsets from host->iomap[PDC_MMIO_BAR]
2. per-port ATA registers, offsets from ap->ioaddr.cmd_addr
3. per-port SATA registers, offsets from ap->ioaddr.scr_addr

The driver currently often fails to indicate which address space
a given mmio base pointer refers to, which is a source of bugs
and confusion (see recent pdc_thaw() irq clearing bug; it's also
been an obstacle for the pending NCQ extensions).

To reduce these problems, adopt a coding style where the name of
a base pointer always indicates which address space it refers to:
1. global registers: host_mmio
2. per-port ATA registers: ata_mmio
3. per-port SATA registers: sata_mmio

Also rearrange register offset definitions to clearly indicate
which address space they belong to, and add a symbolic definition
for the previously hard-coded PHYMODE4 register.
Signed-off-by: Mikael Pettersson <mikpe@it.uu.se>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>