ARM: i.MX: Disable supervisor protect for i.MX51

Most peripherals on the i.MX51 have an Off-Platform Peripheral Access
Control Register (OPACR) in which the access rights (together with the
MPROT registers) can be declared.
However, this does not seem to work for example for SSI1+SDMA, because the
supervisor bit is not set for the SDMA unit.
A similar problem was described in the patch for i.MX53 CPU
(ARM: i.MX53: globally disable supervisor protect), and the same solution
is applicable for i.MX51 CPU.
Patch has tested on custom board based on Digi CCMX-51 module (i.MX51).
Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/mach-imx/mach-imx51.c

@@ -54,6 +54,8 @@ static void __init imx51_dt_init(void)
 	imx_src_init();
 
 	of_platform_populate(NULL, of_default_bus_match_table, NULL, NULL);
+
+	imx_aips_allow_unprivileged_access("fsl,imx51-aipstz");
 }
 
 static void __init imx51_init_late(void)