net: designware: Make driver independent from DM_GPIO again

Commit 90b7fc92 "net: designware: support phy reset device-tree
bindings" made DW GMAC driver dependent on DM_GPIO by unconditional
usage of purely DM_GPIO stuff like:
 * dm_gpio_XXX()
 * gpio_request_by_name()

But since that driver as of today might be easily used without
DM_GPIO (that's the case for Synopsys AXS10x boards) we're
shielding all DM_GPIO things by ifdefs.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Beniamino Galvani <b.galvani@gmail.com>
Cc: Joe Hershberger <joe.hershberger@ni.com>
Cc: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Cc: Sonic Zhang <sonic.zhang@analog.com>
Cc: Bin Meng <bmeng.cn@gmail.com>
Cc: Marek Vasut <marex@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>