riscv: provide a flat image loader

This allows just loading the kernel at a pre-set address without
qemu going bonkers trying to map the ELF file.

Contains a contribution from Aurabindo Jayamohanan to reuse the
PAGE_OFFSET definition.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Anup Patel <anup@brainfault.org>
[paul.walmsley@sifive.com: fixed checkpatch issue; minor commit
 message fix]
Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>

arch/riscv/boot/loader.S

@@ -0,0 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+	.align 4
+	.section .payload, "ax", %progbits
+	.globl _start
+_start:
+	.incbin "arch/riscv/boot/Image"
+