phy: cadence-torrent: Use a common header file for Cadence SERDES

No functional change. In order to have a single header file for all
Cadence SERDES move phy-cadence-torrent.h to phy-cadence.h. This is
in preparation for adding Cadence Sierra SERDES specific macros.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Swapnil Jakhade <sjakhade@cadence.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210319124128.13308-9-kishon@ti.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>