lib: ramdetect: Register exception handlers for ARMv8

Register exception handlers to avoid a Synchronous External Abort
that is raised when you try to access a non-memory address on ARMv8.
An exception handler can jump over the faulting instruction.
This is the feature only for QEMU/AArch64.

Signed-off-by: Asami Doi <d0iasm.pub@gmail.com>
Change-Id: I09a306ca307ba4027d9758c3debc2e7c844c66b8
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34774
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>

src/lib/ramdetect.c

@@ -19,7 +19,7 @@
 
 #define OVERLAP(a, b, s, e) ((b) > (s) && (a) < (e))
 
-static int probe_mb(const uintptr_t dram_start, const uintptr_t size)
+int __weak probe_mb(const uintptr_t dram_start, const uintptr_t size)
 {
 	uintptr_t addr = dram_start + (size * MiB) - sizeof(uint32_t);
 	static const uint32_t patterns[] = {