riscv: Add zihintpause extension support

The zihintpause extension allows software to use the PAUSE instruction to
reduce energy consumption while executing spin-wait code sequences. Add the
zihintpause extension to the device tree if it is supported by the host.

Signed-off-by: Mayuresh Chitale <mchitale@ventanamicro.com>
Link: https://lore.kernel.org/r/20221018140854.69846-4-apatel@ventanamicro.com


Signed-off-by: Will Deacon <will@kernel.org>