configs: phycore_am62x_*_defconfig: Set PHYTEC as Manufacturer

Commit 371b379e ("configs: Make USB_GADGET_MANUFACTURER
consistent over all PHYTEC boards") made the USB_GADGET_MANUFACTURER
value consistent over all PHYTEC boards.

Update the phyCORE-AM62x defconfigs to make this config consistent
as well.

Signed-off-by: Daniel Schultz <d.schultz@phytec.de>