RISC-V irqchip drivers

[Christoph Hellwig]

The RISC-V ISA mandantes the presence of a simple, per-hart (hardware
thread) interrupt controller availiable to supervisor mode.  In addition
the RISC-V specification contains the definition of a programmable
interrupt controller that is present on all current RISC-V cores (at
least as far as a I know).

This series adds both of them.  For the per-hart controller this series
tries to address all comments vs the last posting from Palmr in June,
and for the PLIC it has a lot of cleanups which I think should address
all outstanding comments, but it has been a while since it was last
posted.

Without these irqchip drivers the RISC-V port in mainline is rather
useless as it can't boot on any SOC or emulator.  With it it still is
almost as useless as a clocksource driver is still missing, but at least
we're only a patch or two away from a booting system, and the
clocksource  driver will need the per-hart interrupt driver to work as
well.

Palmer: I assume you are ok with me pushing this forward.  If not I'll
happily drop this series.

A git tree with the patches in this series, the missing clocksource
driver a few pending patches to allow booting a RISC-V kernel in qemu
is available here:

    git://git.infradead.org/users/hch/riscv.git riscv-linux-4.18

Gitweb:

    http://git.infradead.org/users/hch/riscv.git/shortlog/refs/heads/riscv-linux-4.18