igc: set the RX packet buffer size for TSN mode

In preparation for supporting frame preemption, when entering TSN mode,
set the receive packet buffer to 15KB for the Express MAC, 15KB for
the Preemptible MAC and 2KB for the BMC.

References:
I225/I226 SW User Manual, Section 4.7.9, Section 7.1.3.2, Section 8.3.1

The newly introduced macros follow the naming from the i226 SW User Manual
for easy reference.

Co-developed-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Signed-off-by: Faizal Rahim <faizal.abdul.rahim@linux.intel.com>
Tested-by: Mor Bar-Gabay <morx.bar.gabay@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>