Move get_layout() from flashrom.c to layout.c

Change-Id: Ic67cf53abddc0aa905674acbcde717d9aed2f66e
Signed-off-by: David Hendricks <david.hendricks@gmail.com>
Reviewed-on: https://review.coreboot.org/21367
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

layout.h

@@ -58,6 +58,8 @@ struct single_layout {
 };
 
 struct flashrom_layout *get_global_layout(void);
+struct flashrom_flashctx;
+const struct flashrom_layout *get_layout(const struct flashrom_flashctx *const flashctx);
 
 int process_include_args(struct flashrom_layout *);