Revert "rpi4: Enable GENET Ethernet controller"

Revert "rpi4: Enable GENET Ethernet controller"

Since commit 60857f8ec759 ("rpi4: Enable GENET Ehternet controller")
thor downloder fails with log like below:

	U-boot> thordown 0 mmc 0
	TIZEN "THOR" Downloader
	DFU alt info setting: done
	thor_func_set_alt: EPs setup failed!kill ep2out-bulk:  resubmit 4 bytes --> -22thor_init: Data not received!
	THOR DOWNLOAD failed: -1
	WARNING at drivers/usb/gadget/dwc2_udc_otg.c:730/dwc2_free_request()!
	WARNING at drivers/usb/gadget/dwc2_udc_otg.c:730/dwc2_free_request()!

So this disables GENET Ethernet contorller.

Change-Id: I0dd5e5789b0a099768655946122f07ecd1fb609f
Signed-off-by: Dongwoo Lee <dwoo08.lee@samsung.com>