configs: dra74x_evm: rename core_vdd as vdd_core

It is easier to use vdd_core as it remains standard with remaining vdd
rails such as vdd_mpu, gpu etc..

Signed-off-by: Nishanth Menon <nm@ti.com>
configs: dra72x_evm: rename vdd_gpu to vdd_gpu_iva_dspeve

Rename the voltage rail to indicate ganged voltage rail behavior.

Signed-off-by: Nishanth Menon <nm@ti.com>