base: Save and restore the width setting of streams used with cprintf.

base: Save and restore the width setting of streams used with cprintf.

The flags, precision, and fill character were all being saved and
restored, but cprintf might also change the width setting of the
stream, and that wasn't being saved or restored and could leak from
the cprintf statement.

This change adds the code to save and restore that value.

Change-Id: Ibedb26f7f538cd3be4fe0462d2ee4e5efd62bc59
Reviewed-on: https://gem5-review.googlesource.com/12571
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>