image: Use the correct checks for CRC32

image: Use the correct checks for CRC32

Add a host Kconfig for CRC32. With this we can use CONFIG_IS_ENABLED(CRC32)
directly in the host build, so drop the unnecessary indirection.

Add a few more conditions to SPL_CRC32 to avoid build failures as well as
TPL_CRC32. Also update hash.c to make crc32 optional and to actually take
notice of SPL_CRC32.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>