da850evm: Move LPSC configuration to board_early_init_f()

Since commit f1d2b313 the serial
port of the da850evm is accessed before the UART2 peripheral of
the SoC is powered on in the function board_init() in
board/davinci/da8xxevm/da850evm.c.

When u-boot is used in conjunction with the UBL (user boot loader, see
doc/README.davinci) on this board, the UART2 peripheral is already
turned on by UBL at the time u-boot is started. Hence, the wrong
initialization sequence is not noticed by most users. However, if UBL is not
used, u-boot must power on the peripheral before using it.

This patch adds a board_early_init_f() function for the LPSC
configuration to the da850evm board configuration.

Signed-off-by: Christian Riesch <christian.riesch@omicron.at>
Cc: Sudhakar Rajashekhara <sudhakar.raj@ti.com>
Cc: Sandeep Paulraj <s-paulraj@ti.com>
Cc: Heiko Schocher <hs@denx.de>
Cc: Ben Gardiner <bengardiner@nanometrics.ca>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>