dt-bindings: riscv: Add Ssccptr, Sscounterenw, Sstvala, Sstvecd, Ssu64xl

dt-bindings: riscv: Add Ssccptr, Sscounterenw, Sstvala, Sstvecd, Ssu64xl

Add descriptions for five new extensions: Ssccptr, Sscounterenw, Sstvala,
Sstvecd, and Ssu64xl. These extensions are ratified in RISC-V Profiles
Version 1.0 (commit b1d806605f87 "Updated to ratified state.").

They are introduced as new extension names for existing features and
regulate implementation details for RISC-V Profile compliance. According
to RISC-V Profiles Version 1.0 and RVA23 Profiles Version 1.0, their
requirement status are:

 - Ssccptr: Mandatory in RVA20S64, RVA22S64, RVA23S64
 - Sscounterenw: Mandatory in RVA22S64, RVA23S64
 - Sstvala: Mandatory in RVA20S64, RVA22S64, RVA23S64
 - Sstvecd: Mandatory in RVA20S64, RVA22S64, RVA23S64
 - Ssu64xl: Optional in RVA20S64, RVA22S64; Mandatory in RVA23S64

Signed-off-by: Guodong Xu <guodong@riscstar.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>