mm/early_ioremap: Fix boot hang with earlyprintk=efi,keep

earlyprintk=efi,keep does not work any more with a warning
in mm/early_ioremap.c: WARN_ON(system_state != SYSTEM_BOOTING):
Boot just hangs because of the earlyprintk within the earlyprintk
implementation code itself.

This is caused by a new introduced middle state in:

  69a78ff2

 ("init: Introduce SYSTEM_SCHEDULING state")

early_ioremap() is fine in both SYSTEM_BOOTING and SYSTEM_SCHEDULING
states, original condition should be updated accordingly.

Signed-off-by: Dave Young <dyoung@redhat.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: bp@suse.de
Cc: linux-efi@vger.kernel.org
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/20171209041610.GA3249@dhcp-128-65.nay.redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>