ARM: dts: aspeed: romulus: hog GPIOS7

GPIOS7 shall be pulled low for CPLD to continue the power up sequence.
With this hogged as pull-low, the CPLD workaround can be removed in
OpenBMC.

Signed-off-by: Lei YU <mine260309@gmail.com>
Signed-off-by: Joel Stanley <joel@jms.id.au>