phy: cadence-dp: Rename to phy-cadence-torrent

Rename Cadence DP PHY driver from phy-cadence-dp to phy-cadence-torrent
to make it more generic for future use. Modifiy Makefile and Kconfig
accordingly. Also, change driver compatible from "cdns,dp-phy" to
"cdns,torrent-phy".This will not affect ABI as the driver has never
been functional, and therefore do not exist in any active use case.

Signed-off-by: Yuti Amonkar <yamonkar@cadence.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>