net: pcnet: Remove CONFIG_PCNET_79C97x

These macros guard one switch-case statement, which grows mips malta
by some 20 bytes if debug is enabled, and even less if it is not. To
make the code simpler, just support all the NICs and be done with it.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Joe Hershberger <joe.hershberger@ni.com>