powerpc: Dynamically allocate most lppaca structs

powerpc: Dynamically allocate most lppaca structs

This arranges for the lppaca structs for most cpus to be dynamically
allocated in the same manner as the paca structs.  If we don't include
support for legacy iSeries, only the first lppaca is statically
allocated; the rest are dynamically allocated.  If we include legacy
iSeries support, then we statically allocate the first 64 lppaca
structs, since the iSeries hypervisor requires that the lppaca
structs be present in the data section of the kernel image, but
legacy iSeries supports at most 64 cpus.

With CONFIG_NR_CPUS, the kernel image size for a typical pSeries config
went from:

   text    data     bss     dec     hex filename
9524478 4734564 8469944 22728986        15ad11a ../test-1024/vmlinux

to:

   text    data     bss     dec     hex filename
9524482 3751508 8469944 21745934        14bd10e ../test-1024/vmlinux

a reduction of 983052 bytes overall.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>