drm/i915/icl: Introduce new macros to get combophy registers

combo-phy register instances are at same offset from base for each
combo-phy port, i.e.

Port A base offset: 0x16200
Port B base offset: 0x6C000

All the other addresses for both ports can be derived by calculating
offset to these base addresses.

PORT_CL_DW_OFFSET	0x0
PORT_CL_DW<x>		0 + x * 4

PORT_COMP_OFFSET	0x100
PORT_COMP_DW<x>		0x100 + x * 4

PORT_PCS_AUX_OFFSET     0x300
PORT_PCS_GRP_OFFSET     0x600
PORT_PCS_LN<y>_OFFSET   0x800 + y * 0x100

PORT_TX_AUX_OFFSET      0x380
PORT_TX_GRP_OFFSET      0x680
PORT_TX_LN<y>_OFFSET    0x880 + y * 0x100

And inside each PORT_TX_[AUX|GRP|LN] we add `dw * 4`.

Based on original patch by Mahesh Kumar <mahesh1.kumar@intel.com>.

v2: make port, dw and ln arguments follow the order in
    register's name

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Mahesh Kumar <mahesh1.kumar@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181016023517.8576-1-lucas.demarchi@intel.com