[U-Boot] am33xx: Drop timer_init call from s_init - udelay is wrong at ddr configuration

[Egli, Samuel]

Hi Tom, 
I stumbled over your commit b352dde1ea715e8481946ec7d8086b3c3eb126ae
where you removed timer_init() from .../am33xx/board.c.

In the commit message it's written that timer_init will be called 
earlier. However, since this commit udelay will not generate 
correct delays in spl code in our am335xx based boards.
I'm wondering where the timer_init shold be placed. grep-ing 
the code I see that we have a call in spl.c but I this is 
too late. 

Doing some measurements, with this commit udelay is not correct 
at the time of:

 * board_init_ddr()
 * spl_siemens_board_init()

I'm guessing that it might be a problem for other am33xx boards
too, but I didn't verify this.

Right now I just put it back into am33xx/board.c but maybe you
have a better idea.

Kind regards
Sam