i.MX ehci platform support: Some fixes

- The SIC mask is only 2bits wide, not 4
- MX31_OTG_PM_BIT and MX31_H1_PM_BIT use negative logic
- clear MX31_H1_DT_BIT and MX31_H2_DT_BIT so that they can be cleared,
  not only set.
- return -EINVAL if called with an invalid controller number

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Daniel Mack <daniel@caiaq.de>