lib: Add ASan support to romstage on x86 arch

This patch adds ASan support to romstage on x86 architecture.
A Kconfig option is added to enable ASan in romstage. Compiler
flags are updated. A memory space representing the shadow region
is reserved in linker section. And a function call to asan_init()
is added to initialize shadow region when romstage loads.

Change-Id: I67ebfb5e8d602e865b1f5c874860861ae4e54381
Signed-off-by: Harshit Sharma <harshitsharmajs@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/43604
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Werner Zeh <werner.zeh@siemens.com>

src/Kconfig

@@ -288,6 +288,13 @@ if ASAN_IN_RAMSTAGE
 	comment "asan_shadow_offset_callback patch is applied to GCC."
 endif
 
+config ASAN_IN_ROMSTAGE
+	bool
+	depends on ASAN_IN_RAMSTAGE
+	default n
+	help
+	  Enable address sanitizer in romstage for platform.
+
 choice
 	prompt "Stage Cache for ACPI S3 resume"
 	default NO_STAGE_CACHE if !HAVE_ACPI_RESUME