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/include/ramdetect.h

@@ -11,6 +11,12 @@
  * GNU General Public License for more details.
  */
 
+
+/*
+ * Used in probe_ramsize(). This is a weak function and it's overridden for
+ * ARMv8. Return 1 when DRAM exists at the address, otherwise return 0.
+ */
+int probe_mb(const uintptr_t dram_start, const uintptr_t size);
 /*
  * Probe an area if it's read/writable.
  * Primary use case is the detection of DRAM amount on emulators.