[POWERPC] pseries: Force 4k update_flash block and list sizes

[POWERPC] pseries: Force 4k update_flash block and list sizes

The enablement of 64k pages on pseries platforms exposed a bug in
the RTAS mechanism for updating firmware.  RTAS assumes 4k for flash
block and list sizes, and use of any other sizes results in a failure,
even though PAPR does not specify any such requirement.

This patch changes the rtas_flash module to force the use of 4k memory
block and list sizes when preparing and sending a firmware image to
RTAS.  The rtas_flash function now uses a slab cache of 4k blocks with
4k alignment, rather than get_zeroed_page(), to allocate the memory for
the flash blocks and lists.  The 4k alignment requirement is specified
in PAPR.

Signed-off-by: John Rose <johnrose@austin.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>