board: ti: am335x: Conditional MDIO PAD configuration instead of static for AM335_ICE

board: ti: am335x: Conditional MDIO PAD configuration instead of static for AM335_ICE

This patch removes the static MDIO pinmux configuration from
rmii1_pin_mux[] and instead configures the MDIO pins conditionally
during board_init(). Previously, the MDIO_CLK and MDIO_DATA pins
were always configured for CPSW in mux.c, which could lead to
unnecessary pin ownership and conflicts in scenarios where CPSW
is not used.

With this change, the MDIO pins are configured only when required,
ensuring that CPSW Ethernet functionality in U-Boot remains unaffected.
This approach keeps Ethernet boot behavior intact and provides cleaner
separation between CPSW and other Ethernet use cases.

Reviewed-by: Markus Schneider-Pargmann (TI) <msp@baylibre.com>
Signed-off-by: Parvathi Pudi <parvathi@couthit.com>