arch: riscv: drop RISCV_HAS_CPU_IDLE

Because it was exclusively used by the "common" RISC-V privileged code
to build CPU idle routines that are now handled by arch level code.
Also, all platforms defaulted to "y", making it pointless in practice.

Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>
19 files changed