test: shim/system.c system_set/get_scratchpad()
test: shim/system.c system_set/get_scratchpad()

Verify that system_set_scratchpad() saves an arbitrary value and that
system_get_scratchpad() can then subsequently read the set scratchpad.

BRANCH=none
BUG=b:236074898
TEST=twister --clobber -i -s zephyr/test/system_shim/system_shim.default

Signed-off-by: Aaron Massey <79529a820df71f45023239a3663736629646cc34@google.com>
Change-Id: I501fe87db6b5bf4fa588b2422030d68fe25e7ba7
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3931172
Code-Coverage: Zoss <345cf107e82c70959d46f59d98bddc98ce458aff@prod.google.com>
Reviewed-by: Jack Rosenthal <d3f605bef1867f59845d4ce6e4f83b8dc9e4e0ae@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec