Correct SPL uses of CMD_BOOTEFI_BOOTMGR

This converts 3 usages of this option to the non-SPL form, since there is
no SPL_CMD_BOOTEFI_BOOTMGR defined in Kconfig

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>