drivers/usb/host/ohci-hcd: rename readl/writel to ohci_readl/ohci_writel

This avoids a build warning that you see if anyone in the
header chain has included io.h (which is coming shortly).  The previous
code redefined readl/writel; this patch renames it to be specific to
ohci.  The defines are also moved from ohci-hcd.c to ohci.h.

Signed-off-by: Becky Bruce <beckyb@kernel.crashing.org>