[IA64] xenoprof: various fix on linux-xen/perfmon.c

[IA64] xenoprof: various fix on linux-xen/perfmon.c

Various fixes on xen/arch/ia64/linux-xen/perfmon.c
- Fix starting/stopping sampling.
  So far IPI is used. but psr.pp isn't preserved when nested interrupt case
  with VTi domain. Instead timer is used.
- Redefines ia64_set_pmc() to enable sampling of all xen VMM/guest
  kernel/guest user process.  It supports only generic pmc/pmd.
- Twist xenpfm_write_pmcs()
  It is also used when turning on pmcs. So bailing out when error is not
  appropriate. Even when error occures, it should continue to update next
  cpu's pmcs.
- Add gdprintk(XENLOG_DEUBG) and BUG_ON()s.

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>