net: phy: mediatek: fix compile-test dependencies

The new phy driver attempts to select a driver from another subsystem,
but that fails when the NVMEM subsystem is disabled:

WARNING: unmet direct dependencies detected for NVMEM_MTK_EFUSE
  Depends on [n]: NVMEM [=n] && (ARCH_MEDIATEK [=n] || COMPILE_TEST [=y]) && HAS_IOMEM [=y]
  Selected by [y]:
  - MEDIATEK_GE_SOC_PHY [=y] && NETDEVICES [=y] && PHYLIB [=y] && (ARM64 && ARCH_MEDIATEK [=n] || COMPILE_TEST [=y])

I could not see an actual compile time dependency, so presumably this
is only needed for for working correctly but not technically a dependency
on that particular nvmem driver implementation, so it would likely
be safe to remove the select for compile testing.

To keep the spirit of the original 'select', just replace this with a
'depends on' that ensures that the driver will work but does not get in
the way of build testing.

Fixes: 98c485ea

 ("net: phy: add driver for MediaTek SoC built-in GE PHYs")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Reviewed-by: Daniel Golle <daniel@makrotopia.org>
Link: https://lore.kernel.org/r/20230616093009.3511692-1-arnd@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>