ofw_cpu: fix __riscv preprocessor check

[mhorne]

Summary

The canonical name is riscv, not riscv__. Newer compilers no longer
emit the latter.

This re-enables finding the nominal frequency from the CPU's clock.

I checked, and there are no remaining mistakes like this in the tree.

[imp]

Do we need to update arch(7)?

[mhorne]

In D48122#1097216, @imp wrote:

Do we need to update arch(7)?

No, that seems to be correct already.

[jrtc27]

From grepping the tree this doesn't actually have any consequences currently, right, other than possible prints? The only real use I see is cpufreq, which we don't currently have for RISC-V.

[jhb]

sys/dev/ofw/ofw_cpu.c

279

If we moved the variable declarations to here, would that reduce the need for the second #if above? That might be preferable as a followup commit to keep the number of #if's down.

[imp]

sys/dev/ofw/ofw_cpu.c

46

Add

#define HAS_CLOCK

here. Ideally this would be global, but that makes this change too large.

(of course, this is tweaking an otherwise boring tweak, so maybe a followup)

209

#ifdef HAS_CLOCK

279

#ifdef HAS_CLOCK

[imp]

My suggestions likely are out of scope, though...

[mhorne]

sys/dev/ofw/ofw_cpu.c

46

Yes, ideally a global coming from the kernel config. Leaving that part for another day :)

279

D48149. I will still commit this one as-is first, somewhat redundantly.