MIPS: generic: Fix KASLR for generic kernel.

The KASLR code requires that the plat_get_fdt() function return the
address of the device tree, and it must be available early in the boot,
before prom_init() is called. Move the code determining the address of
the device tree into plat_get_fdt, and call that from prom_init().

The fdt pointer will be set up by plat_get_fdt() called from
relocate_kernel initially and once the relocated kernel has started,
prom_init() will use it again to determine the address in the relocated
image.

Fixes: eed0eabd12ef ("MIPS: generic: Introduce generic DT-based board support")
Signed-off-by: Matt Redfearn <matt.redfearn@imgtec.com>
Reviewed-by: James Hogan <james.hogan@imgtec.com>
Reviewed-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/14415/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/generic/init.c

@@ -29,10 +29,20 @@ static __initdata const struct mips_machine *mach;
 static __initdata const void *mach_match_data;
 
 void __init prom_init(void)
+{
+	plat_get_fdt();
+	BUG_ON(!fdt);
+}
+
+void __init *plat_get_fdt(void)
 {
 	const struct mips_machine *check_mach;
 	const struct of_device_id *match;
 
+	if (fdt)
+		/* Already set up */
+		return (void *)fdt;
+
 	if ((fw_arg0 == -2) && !fdt_check_header((void *)fw_arg1)) {
 		/*
 		 * We booted using the UHI boot protocol, so we have been
@@ -75,12 +85,6 @@ void __init prom_init(void)
 		/* Retrieve the machine's FDT */
 		fdt = mach->fdt;
 	}
-
-	BUG_ON(!fdt);
-}
-
-void __init *plat_get_fdt(void)
-{
 	return (void *)fdt;
 }