board: am64x: Use generic AM6x board detection functions

board: am64x: Use generic AM6x board detection functions

Replace the board-specific implementation of do_board_detect() and
setup_serial() with calls to the generic do_board_detect_am6() and
setup_serial_am6() functions.

The generic function provides the same functionality with
additional fallback logic to try alternate EEPROM addresses.

Reviewed-by: Mattijs Korpershoek <mkorpershoek@kernel.org>
Signed-off-by: Guillaume La Roque (TI.com) <glaroque@baylibre.com>