Revert "sdhci: extend bus_dma_tag boundary to 64-bit space"

This reverts commit 7d8700bc291b4b3be1a592cae539f9e682592d9d.

Reason for revert: the patch is incomplete. 64-bit operation
is supported fully in SDHCI v4.0, v3.0 does it only for ADMA mode.
This differentiation is missing and should be taken into consideration
in case the reverted code is re-introduced.

Reported by: mmel