[POWERPC] PS3: Fix printing of os-area magic numbers

Fix a bug in the printing of the os-area magic numbers which assumed
that magic numbers were zero terminated strings.  The magic numbers
are represented in memory as integers.  If the os-area sections are
not initialized correctly they could contained random data that would
be printed to the display.  Also unify the handling of header and db
magic numbers and make both of type array of u8.

Signed-off-by: Geoff Levand <geoffrey.levand@am.sony.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>