For some unknown reason, allowing hwmod to control MIDLEMODE causes
core_pwrdm to not hit idle states for musb in DM3730 at least.
I've verified that setting any MIDLEMODE value other than "force
standby" before enabling the device causes subsequent suspend
attempts to fail with core_pwrdm not entering idle states, even
if the driver is unloaded and "force standby" is restored before
suspend attempt. To recover from this, soft reset can be used, but
that's not suitable solution for suspend.

Keeping the register set at force standby (reset value) makes it work
and device still functions properly, as musb has driver-controlled
OTG_FORCESTDBY register that controls MSTANDBY signal.
Note that TI PSP kernels also have similar workarounds.

This patch also fixes HWMOD_SWSUP_MSTANDBY documentation to match the
actual flag name.
Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>