ARM: dts: dra7: Fix suspend warning for vpe powerdomain

We currently are getting the following warning after a system suspend:

Powerdomain (vpe_pwrdm) didn't enter target state 0

Looks like this is because the STANDBYMODE bit for SMART_IDLE should
not be used. The TRM "Table 12-348. VPE_SYSCONFIG" says that the value
for SMART_IDLE is "0x2: Same behavior as bit-field value of 0x1". But
if the SMART_IDLE value is used, PM_VPE_PWRSTST LASTPOWERSTATEENTERED
bits always show value of 3.

Let's fix the issue by dropping SMART_IDLE for vpe. And let's also add
the missing the powerdomain for vpe.

Fixes: 1a209516 ("ARM: dts: dra7: Add ti-sysc node for VPE")
Cc: Benoit Parrot <bparrot@ti.com>
Reported-by: Kevin Hilman <khilman@baylibre.com>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Tested-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>