powerpc/eeh: Initialize EEH address cache earlier

powerpc/eeh: Initialize EEH address cache earlier

The EEH address cache is currently initialized and populated by a
single function: eeh_addr_cache_build().  While the initial population
of the cache can only be done once resources are allocated,
initialization (just setting up a spinlock) could be done much
earlier.

So move the initialization step into a separate function and call it
from a core_initcall (rather than a subsys initcall).

This will allow future work to make use of the cache during boot time
PCI scanning.

Signed-off-by: Sam Bobroff <sbobroff@linux.ibm.com>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/0557206741bffee76cdfff042f65321f6f7a5b41.1565930772.git.sbobroff@linux.ibm.com