mmc: sdhci-omap: Add omap_offset to support omap3 and earlier

mmc: sdhci-omap: Add omap_offset to support omap3 and earlier

The omap specific registers are at offset 0x100 from base for omap4 and
later, and for omap3 and earlier they are at offset 0. Let's handle also
the earlier SoCs by adding omap_offset.

Note that eventually we should just move to using standard sdhci register
access for the sdhci range with new offsets starting at 0x100.

Signed-off-by: Tony Lindgren <tony@atomide.com>
Link: https://lore.kernel.org/r/20211015104720.52240-4-tony@atomide.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>