ARM: OMAP2+: omap4-panda: add UART2 muxing for WiLink shared transport

Add the UART2 muxing data to the board file (this used to be,
erroneously, done in the bootloader).

Cc: stable <stable@vger.kernel.org> [3.7]
Signed-off-by: Luciano Coelho <coelho@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>