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Subjectsimplified RISC-V interrupt and clocksource handling v3
This series tries adds support for interrupt handling and timers
for the RISC-V architecture.

The basic per-hart interrupt handling implemented by the scause
and sie CSRs is extremely simple and implemented directly in
arch/riscv/kernel/irq.c. In addition there is a irqchip driver
for the PLIC external interrupt controller, which is called through
the set_handle_irq API, and a clocksource driver that gets its
timer interrupt directly from the low-level interrupt handling.

Compared to previous iterations this version does not try to use an
irqchip driver for the low-level interrupt handling. This saves
a couple indirect calls and an additional read of the scause CSR
in the hot path, makes the code much simpler and last but not least
avoid the dependency on a device tree for a mandatory architectural

A git tree is available here (contains a few more patches before
the ones in this series)

git:// riscv-irq-simple.3


Changes since v2:
- actually use SEIE instead of STIE in the plic driver
- rename the default compat string for the plic to sifive,u5-plic
- various spelling fixes
- drop a superflous derefence in the plic driver that is taken care of
by the following loop
- drop the patch to document the enable method - not relevant for the
rest of the series
- drop the patches for the per-hart timebase frequency - not relevant
for the rest of the series.
- use riscv_of_processor_hart in the timer driver

Changes since v1:
- rename the plic driver to irq-sifive-plic
- switch to a default compatible of sifive,plic0 (still supporting the
riscv,plic0 name for compatibility)
- add a reference for the SiFive PLIC register layout
- fix plic_toggle addressing for large numbers of hwirqs
- remove the call to ack_bad_irq
- use a raw spinlock for plic_toggle_lock
- use the irq_desc cpumask in the plic enable/disable methods
- add back OF contexid parsing in the plic driver
- don't allow COMPILE_TEST builds of the clocksource driver, as it
depends on <asm/sbi.h>
- default the clocksource driver to y
- clean up naming in the clocksource driver
- remove the MINDELTA and MAXDELTA #defines
- various DT binding fixes

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