c6x: convert fdt pointers to opaque pointers

The architecture code does not need to access the internals of the FDT
blob, so make the pointer to it void *.
Signed-off-by: NRob Herring <robh@kernel.org>
Cc: Mark Salter <msalter@redhat.com>
Cc: Aurelien Jacquiot <a-jacquiot@ti.com>
Cc: linux-c6x-dev@linux-c6x.org
Tested-by: NGrant Likely <grant.likely@linaro.org>

arch/c6x/kernel/setup.c

@@ -265,8 +265,8 @@ int __init c6x_add_memory(phys_addr_t start, unsigned long size)
  */
 notrace void __init machine_init(unsigned long dt_ptr)
 {
-	struct boot_param_header *dtb = __va(dt_ptr);
-	struct boot_param_header *fdt = (struct boot_param_header *)_fdt_start;
+	const void *dtb = __va(dt_ptr);
+	const void *fdt = _fdt_start;
 
 	/* interrupts must be masked */
 	set_creg(IER, 2);