Introduce a common delay function to provide flexible way for users to take
choices of udelay and usleep_range into consideration according to the
required delay time.

Link: https://lore.kernel.org/r/20200318104016.28049-4-stanley.chu@mediatek.comReviewed-by: Avri Altman <avri.altman@wdc.com>
Reviewed-by: Can Guo <cang@codeaurora.org>
Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>