bootstd: Add the bootstd uclass and core implementation

The 'bootstd' device provides the central information about U-Boot
standard boot.

Add a uclass for bootstd and the various helpers needed to make it
work. Also add a binding file.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/efi-x86_app32_defconfig b/configs/efi-x86_app32_defconfig
index 228643a..7a723c1 100644
--- a/configs/efi-x86_app32_defconfig
+++ b/configs/efi-x86_app32_defconfig
@@ -8,6 +8,7 @@
 CONFIG_TARGET_EFI_APP32=y
 CONFIG_DEBUG_UART=y
 CONFIG_FIT=y
+# CONFIG_BOOTSTD is not set
 CONFIG_SHOW_BOOT_PROGRESS=y
 CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS="root=/dev/sdb3 init=/sbin/init rootwait ro"