mmc: sdhci-tegra: cleanup ifdefs

The structs wrapped with the SOC ifdefs are small enough where having
them always there shouldn't be a big overhead. Removing the ifdefs
also makes the code a little cleaner.

Signed-off-by: Rhyland Klein <rklein@nvidia.com>
Acked-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Chris Ball <cjb@laptop.org>