Fix minor locking issues in the PowerMac Uninorth PCI driver

[landonf]

Summary

• Call resource_int_value() once during attach, rather than within the pci_(read|write)_config() code path; this avoids taking a blocking mutex to read kenv variables.
• Use a spin lock to protect non-atomic config space accesses (this matches the behavior of the Darwin AppleMacRiscPCI driver).

Test Plan

Tested for regressions on a PowerBook5,8.

[landonf]

• Add mtx_assert(MA_OWNED) to uninorth_enable_config() for good measure.

[jhibbits]

sys/powerpc/powermac/uninorthvar.h

43 ↗

(On Diff #37760)

Match whitespace? Might be phabricator messing with it, but just double check.

[landonf]

sys/powerpc/powermac/uninorthvar.h

43 ↗

(On Diff #37760)

Yeah, looks like phabricator behaving badly.