Introduce an `include` directory for header files

Move all header files to the new `include` directory.
Adapt include directives and build systems to the new directory.

Change-Id: Iaddd6bbfa0624b166d422f665877f096983bf4cf
Signed-off-by: Felix Singer <felix.singer@secunet.com>
Signed-off-by: Thomas Heijligen <thomas.heijligen@secunet.com>
Original-Reviewed-on: https://review.coreboot.org/c/flashrom/+/58622
Original-Reviewed-by: Anastasia Klimchuk <aklm@chromium.org>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/72322
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Felix Singer <felixsinger@posteo.net>
diff --git a/util/ich_descriptors_tool/Makefile b/util/ich_descriptors_tool/Makefile
index ea80dc6..0b8a210 100644
--- a/util/ich_descriptors_tool/Makefile
+++ b/util/ich_descriptors_tool/Makefile
@@ -21,6 +21,7 @@
 # If the user has specified custom CFLAGS, all CFLAGS settings below will be
 # completely ignored by gnumake.
 CFLAGS ?= -Os -Wall -Wshadow
+CFLAGS += -I$(SHAREDSRCDIR)/include
 
 # Auto determine HOST_OS and TARGET_OS if they are not set as argument
 HOST_OS ?= $(shell uname)