lib: os: add CRC shell command for integrity verification

There are several Zephyr shell commands that are used for
transferring data over a possibly unreliable connection such as a
UART into either memory or flash. For example, `flash load` and
`devmem load`.

Make the CRC functions available so that they can be used to
verify the integrity of data transferred over possibly
unreliable connections.

Signed-off-by: Chris Friedt <cfriedt@meta.com>