Revert "phy: Add USB3 PHY support for Broadcom NSP SoC"

This reverts commit d7bc1a7d ("phy: Add USB3 PHY support for
Broadcom NSP SoC") as we already have driver for this PHY (shared by NS
and NSP). It was added in commit e5666281 ("phy: bcm-ns-usb3: new
driver for USB 3.0 PHY on Northstar").

Instead of adding separated driver & duplicating code we should work on
improving existing (old) one. Thanks to work done by Broadcom we know
there is MDIO bus we weren't aware of & we know register names which
makes initialization more clear. This is very valuable info and we
should work on using it in existing driver afterwards.

Acked-by: Jon Mason <jon.mason@broadcom.com>
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>