ARM: dts: STi: Add gpio polarity for "hdmi,hpd-gpio" property

The GPIO polarity is missing in the hdmi,hpd-gpio property, this
fixes the following DT warnings:

arch/arm/boot/dts/stih410-b2120.dtb: Warning (gpios_property): hdmi,hpd-gpio property
size (8) too small for cell size 2 in /soc/sti-display-subsystem/sti-hdmi@8d04000

arch/arm/boot/dts/stih407-b2120.dtb: Warning (gpios_property): hdmi,hpd-gpio property
size (8) too small for cell size 2 in /soc/sti-display-subsystem/sti-hdmi@8d04000

arch/arm/boot/dts/stih410-b2260.dtb: Warning (gpios_property): hdmi,hpd-gpio property
size (8) too small for cell size 2 in /soc/sti-display-subsystem/sti-hdmi@8d04000

[arnd: marked Cc:stable since this warning shows up with the latest dtc
       by default, and is more likely to actually cause problems than the
       other patches from this series]

Cc: stable@vger.kernel.org
Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>