ASoC: Intel: avs: Cleanup duplicate members

Switch to the new board registration functions and remove the
then-unused code.

The SSP-number-check is still important and cannot be just dropped. Move
it from avs_register_i2s_board(), which is being removed with this
patch, to avs_register_i2s_boards() to maintain sanity when registering
a board.

Reviewed-by: Amadeusz Sławiński <amadeuszx.slawinski@linux.intel.com>
Signed-off-by: Cezary Rojewski <cezary.rojewski@intel.com>
Message-ID: <20250827142229.869139-3-cezary.rojewski@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>