ARM: OMAP4: USB: Update workaround for USB errata i719

Due to USB errata i719 the USB host save-and-restore context can be corrupted
if the device enters off mode more than two times without enabling the USB
host controller in between.

The corruption is occuring during the software save of the USB context which
occurs on entry to every off mode attempt. To avoid this problem only save the
USB context if the USB host controller has been enabled since the previous off
mode attempt. We do not need to save the USB context on every entry to off mode
if the USB controller has not been enabled.

Change-Id: I67e07963679af6494ef289eb10db09c0162d6f00
Signed-off-by: Jon Hunter <jon-hunter@ti.com>
Signed-off-by: Volodymyr Riazantsev <v.riazantsev@ti.com>
Signed-off-by: Ruslan Bilovol <ruslan.bilovol@ti.com>