[IA64] fix early access to per cpu area.

[IA64] fix early access to per cpu area.

The following changeset broke booting xen-ia64 on some kinds of ia64 boxes.
http://xenbits.xensource.com/ext/ia64/xen-unstable.hg/rev/3fd8f9b34941

The tasklet_schedule call raise_softirq().
Because raise_softirq() use per_cpu, if we access per_cpu before cpu_init()
the behavior would be unexpected.

There was a similar issue on Linux/ia64.
The following change sets resolved it.
	10617bbe84628eb18ab5f723d3ba35005adde143
	c459ce8b5a7d933a3bcf6915ab17ac1e036e2ac4

This patch fixes the issue following the linux/ia64 solution.
Allocate per cpu area for cpu0 in .data section and initialize
it early.

reported-by: Akio Takebe <takebe_akio@jp.fujitsu.com>
Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
--HG--
rename : xen/include/asm-ia64/linux/asm/sections.h => xen/include/asm-ia64/linux-xen/asm/sections.h