dt-bindings: riscv: Add SiFive HiFive Premier P550 board

dt-bindings: riscv: Add SiFive HiFive Premier P550 board

Add DT binding documentation for the ESWIN EIC7700 SoC and
HiFive Premier P550 Board

Signed-off-by: Pritesh Patel <pritesh.patel@einfochips.com>
Reviewed-by: Samuel Holland <samuel.holland@sifive.com>
Signed-off-by: Pinkesh Vaghela <pinkesh.vaghela@einfochips.com>
Reviewed-by: Matthias Brugger <matthias.bgg@kernel.org>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Acked-by: Min Lin <linmin@eswincomputing.com>
Link: https://lore.kernel.org/r/20250825132427.1618089-4-pinkesh.vaghela@einfochips.com
Signed-off-by: Arnd Bergmann <arnd@arndb.de>