ethernet: ucc_geth: don't statically allocate eight ucc_geth_info

struct ucc_geth_info is somewhat large, and on systems with only one
or two UCC instances, that just wastes a few KB of memory. So
allocate and populate a chunk of memory at probe time instead of
initializing them all during driver init.

Note that the existing "ug_info == NULL" check was dead code, as the
address of some static array element can obviously never be NULL.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>