mmc: pci_mmc.c should build with ACPIGEN=n

sandbox_defconfig builds the PCI MMC driver. It should be possible to
build the sandbox without ACPI support.

ACPI support in the PCI MMC driver is only needed when creating an ACPI
table. Fix building with ACPIGEN=n.

Fixes: dba7ee41 ("acpi: mmc: Generate ACPI info for the PCI SD Card")
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>