dt-bindings: riscv: Add SiFive P550 CPU compatible

Update Documentation for supporting SiFive P550 based CPU

Signed-off-by: Darshan Prajapati <darshan.prajapati@einfochips.com>
Reviewed-by: Samuel Holland <samuel.holland@sifive.com>
Signed-off-by: Pinkesh Vaghela <pinkesh.vaghela@einfochips.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20250825132427.1618089-2-pinkesh.vaghela@einfochips.com


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