MFC r311911, r311923

r311911:
[sdhci] Add ACPI platform support for SDHCI driver

• Create ACPI version of SDHCI attach/detach/accessors logic. Some platforms (e.g. BayTrail-based Minnowboard) expose SDHCI devices via ACPI, not PCI
• Add sdchi_acpi kernel module

Reviewed by: ian, imp
Differential Revision: https://reviews.freebsd.org/D9112

r311923:
Add acpi_if.h and opt_acpi.h to Makefile to unbreak "make depend" with
sys/modules/sdhci_acpi

X-MFC with: r311911
Reported by: Jenkins