Add delay timer API so that it can be called by delay timer
layer and used as delay timer globally.

[bod: changed name from imx_delay_timer -> imx_gpt ]
Signed-off-by: Jun Nie <jun.nie@linaro.org>
Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>