Add a Kconfig to selectively enable the AMD Picasso eMMC driver recently added to MrChromebox's edk2 fork. When selected, will enable booting from AMD Picasso devices with eMMC storage. TEST=tested with rest of patch train Change-Id: I6536a6f243f6766b913e295afebcf5b965e4e969 Signed-off-by: Matt DeVillier <matt.devillier@gmail.com> Reviewed-on: https://review.coreboot.org/c/coreboot/+/81892 Reviewed-by: Sean Rhodes <sean@starlabs.systems> Tested-by: build bot (Jenkins) <no-reply@coreboot.org>