xen/arm64: head: Mark the end of subroutines with ENDPROC

putn() and puts() are two subroutines. Add ENDPROC for the benefits of
static analysis tools and the reader.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

xen/arch/arm/arm64/head.S

@@ -638,6 +638,7 @@ puts:
         b     puts
 1:
         ret
+ENDPROC(puts)
 
 /* Print a 32-bit number in hex.  Specific to the PL011 UART.
  * x0: Number to print.
@@ -656,6 +657,7 @@ putn:
         subs  x3, x3, #1
         b.ne  1b
         ret
+ENDPROC(putn)
 
 hex:    .ascii "0123456789abcdef"
         .align 2