microblaze: defconfig: Enable the Marvell phy driver

Enable the marvell phy driver by default as it is commonly
used PHY on multiple microblaze based evaluation boards.

Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/3912fb168671dd5b418da8947ea1c463b554fa86.1698155190.git.michal.simek@amd.com