ARM: bcm283x: Switch to generic timer

Switch to generic timer implementation from lib/time.c .
This also fixes a signed overflow which was in __udelay()
implementation.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Stephen Warren <swarren@wwwdotorg.org>
Cc: Tyler Baker <tyler.baker@linaro.org>
Acked-by: Stephen Warren <swarren@wwwdotorg.org>