usb: dwc3: omap: Adds dwc3_omap_readl/writel wrappers

This patch adds wrappers to dwc3_omap_readl/writel calls to accomodate
both OMAP5 and AM437x reg maps (It uses the cached register offsets).
Also renames OMAP5 IRQ1 as IRQMISC and IRQ1 bits as IRQMISC bits.

Signed-off-by: George Cherian <george.cherian@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>