riscv/mb/qemu: fix DRAM probing

Current version of qemu raise an exception when accessing invalid
memory.  Modify the probing code to temporary redirect the exception
handler like on ARM platform.
Also move saving of the stack frame out to trap_util.S to have all at
the same place for a future rewrite.

TEST=boots to ramstage
Change-Id: I25860f688c7546714f6fdbce8c8f96da6400813c
Signed-off-by: Philipp Hug <philipp@hug.cx>
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/36486
Reviewed-by: ron minnich <rminnich@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

0 files changed, 0 insertions, 0 deletions