ARM: dts: spear3xx: Add spear320s dtsi

The SPEAr320s SOC is a SPEAr320 SOC variant.

Mostly identical to the SPEAr320 SOC variant, it has a
new interrupt routing for PL_PGIOs.

Add spear320s.dtsi to handle SPEAr320s SOC

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Link: https://lore.kernel.org/r/20211202095255.165797-7-herve.codina@bootlin.com

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Signed-off-by: Arnd Bergmann <arnd@arndb.de>