s390: Use arch_local_irq_{save,restore}() in early boot code

Commit 997acaf6 ("lockdep: report broken irq restoration") makes
compiling s390 fail because the irq enable/disable functions are now
no longer fully contained in header files.

Fixes: 997acaf6 ("lockdep: report broken irq restoration")
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>