dm: pch: Remove pch_get_version op

pch_get_version op was only used by the ich spi controller driver,
and does not really provide a good identification of pch controller
so far, since we see plenty of Intel PCH chipsets and one differs
from another a lot, which is not simply either a PCHV_7 or PCHV_9.
Now that ich spi controller driver was updated to not get such info
from pch, the pch_get_version op is useless now.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>