RISC-V: Add FIRMWARE_READ_HI definition

RISC-V: Add FIRMWARE_READ_HI definition

SBI v2.0 added another function to SBI PMU extension to read
the upper bits of a counter with width larger than XLEN.

Add the definition for that function.

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Clément Léger <cleger@rivosinc.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Link: https://lore.kernel.org/r/20240420151741.962500-3-atishp@rivosinc.com
Signed-off-by: Anup Patel <anup@brainfault.org>