libpayload: Make Kconfig bools use IS_ENABLED()

This will make the code work with the different styles
of Kconfig (emit unset bools vs don't emit unset bools)

Roughly, the patch does this, and a little bit of fixing up:

perl -pi -e 's,ifdef (CONFIG_LP_.+?)\b,if IS_ENABLED\($1\),g' `find . -name *.[ch]`
perl -pi -e 's,ifndef (CONFIG_LP_.+?)\b,if !IS_ENABLED\($1\),g' `find . -name *.[ch]`

Change-Id: Ib8a839b056a1f806a8597052e1b571ea3d18a79f
Signed-off-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-on: http://review.coreboot.org/10711
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

payloads/libpayload/drivers/usb/usbhid.c

@@ -138,7 +138,7 @@ struct layout_maps {
 static const struct layout_maps *map;
 
 static const struct layout_maps keyboard_layouts[] = {
-// #ifdef CONFIG_LP_PC_KEYBOARD_LAYOUT_US
+// #if IS_ENABLED(CONFIG_LP_PC_KEYBOARD_LAYOUT_US)
 { .country = "us", .map = {
 	{ /* No modifier */
 	-1, -1, -1, -1, 'a', 'b', 'c', 'd',