[RFC] SDHCI driver split

[Oleksandr Tymoshenko]

Hello,

Proposed patch[1] splits sdhci driver in two parts: reusable SDHCI 
logic and PCI driver that provides access to registers. 

I tested it on X220 with Ricoh controller - no performance regression:
reading 4Gb card takes 180 seconds (+/- 2) for both versions, old and new. 

If there are no objections - I'll commit it later this week. 

[1] http://people.freebsd.org/~gonzo/patches/sdhci-pci-3.diff