davinci: Rewrite timer.c to use tbl/tbu emulation variables in gd

davinci: Rewrite timer.c to use tbl/tbu emulation variables in gd

This change allows the davinci timer functions to be used before
relocation since it avoids using static variables prior to BSS being
made available.

The code is based on that used in the at91 timers, modified to use
a davinci specific hardware timer. It also maintains reset_timer()
to allow deprecated timer usage to continue to work (for example,
in nand_base.c)

Signed-off-by: Nick Thompson <nick.thompson@ge.com>
Tested-by: Ben Gardiner <bengardiner@nanometrics.ca>
Tested-by: Sudhakar Rajashekhara <sudhakar.raj@ti.com>
Tested-by: Sandeep Paulraj <s-paulraj@ti.com>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>