powerpc/64: Invalidate process table caching after setting process table

The POWER9 MMU reads and caches entries from the process table.
When we kexec from one kernel to another, the second kernel sets
its process table pointer but doesn't currently do anything to
make the CPU invalidate any cached entries from the old process table.
This adds a tlbie (TLB invalidate entry) instruction with parameters
to invalidate caching of the process table after the new process
table is installed.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>