MIPS: RB532: Avoid undefined mac_pton without GENERIC_NET_UTILS

Currently MIPS allnoconfig with CONFIG_MIKROTIK_RB532=y fails to link
due to missing support for mac_pton():

  LD      vmlinux
arch/mips/rb532/devices.o: In function `setup_kmac':
devices.c:(.init.text+0xc): undefined reference to `mac_pton'

Rather than adding dependencies to the platform to force inclusion of
GENERIC_NET_UTILS which is selected by CONFIG_NET, just exclude the
setup of the MAC address if CONFIG_NET is not selected in the kernel
config.

Signed-off-by: Matt Redfearn <matt.redfearn@mips.com>
Cc: James Hogan <james.hogan@mips.com>
Cc: Boris Brezillon <boris.brezillon@free-electrons.com>
Cc: Neil Armstrong <narmstrong@baylibre.com>
Cc: Krzysztof Kozlowski <krzk@kernel.org>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Vladimir Zapolskiy <vz@mleia.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/17702/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>