coreboot/Makefile: display error when spaces in path of toplevel makefile

coreboot toplevel makefile breaks when path to the coreboot directory
contains spaces.
This patch displays a reasonable message to the user whenever spaces
are found within the path to the coreboot direcrory.

This commit addresses coreboot ticket #179.

Change-Id: Id11deffa01ddca1ff9332d67c7aa33a382b4cdc7
Signed-off-by: Sourabh Kashyap <sourabhka@hcl.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/35434
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

Makefile

@@ -30,6 +30,9 @@
 ## SUCH DAMAGE.
 ##
 
+ifneq ($(words $(CURDIR)),1)
+    $(error Error: Path to the main directory cannot contain spaces)
+endif
 top := $(CURDIR)
 src := src
 srck := $(top)/util/kconfig