Introduce the SDHCI driver for NXP QorIQ Layerscape SoCs

Implement support for an eSDHC controller found in NXP QorIQ Layerscape SoCs.

This driver has been tested with NXP LS1046A and LX2160A (Honeycomb board),
which is incompatible with the existing sdhci_fsl driver (aiming at older
chips from this family). As such, it is not intended as replacement for
the old driver, but rather serves as an improved alternative for SoCs that
support it.
It comes with support for both PIO and Single DMA modes and samples the
clock from the extres clk API.

Submitted by: Artur Rojek <ar@semihalf.com>
Reviewed by: manu, mmel, kibab
Obtained from: Semihalf
Sponsored by: Alstom Group
Differential Revision: https://reviews.freebsd.org/D26153