[POWERPC] re-enable OProfile for iSeries, using timer interrupt

This patch removes the changes from an earlier patch that disables
oProfile for iSeries within the oProfile KConfig (submitted Feb 23,
2006).  Checks within the arch init for iSeries, still allowing profiling
for timer interrupts (using firmware_has_feature).

Signed-off-by: Kelly Daly <kelly@au.ibm.com>
Acked-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>