xen spl rework

["Cherry G. Mathew" <cherry.g.mathew%gmail.com@localhost>]

Hi,

I've reworked the spl code in XEN to use a single entry point into C
code, and to optimise the pending event processing via spllower()

See:
ftp://ftp.netbsd.org/pub/NetBSD/misc/cherry/tmp/port-xen/spl.diff

I'd love for as much test reportage as possible with this patch.

dom0 is reported to hang on launching domUs. I'd like this verified on
PAE kernels if possible.

Please include relevant dmesg/console output.

tech-kern@ is Cc:ed for more eyes to see if I've missed anything obvious.
port-i386/amd64@ is Cc:ed because I've removed some of the common
assembler bits from the XEN path and added some new. Review would be
useful. I'm hoping this doesn't affect anything for non-XEN.

Many Thanks,

-- 
~Cherry