Merge https://gitlab.denx.de/u-boot/custodians/u-boot-x86

- Enable SD slot on Intel Edison
- Populate CSRT ACPI table for shared DMA controller on Intel Tangier
- Convert Intel ICH-SPI driver to use new spi-mem ops
- Enable config_distro_bootcmd for QEMU x86
- Support U-Boot as a payload for Intel Slim Bootloader
- Avoid writing temporary asl files into the source tree which fixes the
  parallel build issue occasionally seen