util/cbmem: Use commonlib ipchksum() algorithm

util/cbmem: Use commonlib ipchksum() algorithm

This patch switches the cbmem utility from its own IP checksum
implementation to the commonlib version (which is good because the old
one had a couple of bugs: doesn't work on odd sizes and may overflow
its carry accumulator with input larger than 64K).

Change-Id: I0bef2c85c37ddd3438b7ac6389e9daa3e4955b31
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/80256
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Yidi Lin <yidilin@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>