configs: j721e_hs_evm_a72_defconfig: Add command for initializing QSGMII PHY

QSGMII PHY present on the j721e common processor board requires
to be initialized before the core boots up. Therefore, run the
corresponding command during boot to do the same.

Signed-off-by: Aswath Govindraju <a-govindraju@ti.com>