powerpc64: fix radix on pseries TLB invalidation

[luporl]

Summary

When running in a virtualized environment, TLB invalidations can only
be performed on process scope, as only the hypervisor is allowed to
invalidate a global scope, or else a Program Interrupt is triggered.

Since we are here, also make sure that the register process table
hypercall returns success.

Test Plan

Tested on QEMU with KVM enabled, on a POWER9 machine.
(currently depends on a patched loader version to work, to call CAS and select Radix with GTSE)

[jhibbits]

Glad to see you solve the last piece of this puzzle!

sys/powerpc/aim/mmu_radix.c

761–765

Can TLB_INVAL_SCOPE_* be renumbered to 2/3 instead of 0/1? That would avoid needing to pass the scope as extra.

[luporl]

• Address reviewer's comments