libbootmsg: Do not use '\b' characters when printing checkpoints

Using backspaces after printing out the checkpoint numbers is fine
when printing to terminals. But if the output of SLOF is placed
into a log file instead, this can confuse certain readers like
Firefox to interpret the log file as a binary file instead of text.
To avoid this problem, we can also use '\r' to move the cursor
back to the beginning - this should be fine since the checkpoints
are always printed at the beginning of a line anyway. And '\r' is
then interpreted as normal text, not as a potential binary file byte.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>

lib/libbootmsg/bootmsg_lvl.S

@@ -58,10 +58,8 @@ ENTRY(bootmsg_cp)
 	bl      io_putchar      // print character
 	mr	r3, r9
 	bl      io_printhex16   // print checkpoint ID
-	.rept   5
-	li      r3,'\b'
-	bl      io_putchar      // print backspaces
-	.endr
+	li      r3,'\r'
+	bl      io_putchar      // go back
 	mtlr	r11
 	blr