openrisc: Add support for external initrd images

In OpenRISC we set the initrd_start and initrd_end based on the symbols
we setup in vmlinux.lds.S.  However, this is not needed if we use the
generic linker description in INIT_DATA_SECTION.

Removing our own initrd setup reduces code, but also the generic code
supports loading external initrd images.  A bootloader can load a rootfs
image into memory and we can configure devicetree to load it with:

        chosen {
                bootargs = "earlycon";
                stdout-path = "uart0:115200";
                linux,initrd-start = < 0x08000100 >;
                linux,initrd-end = < 0x08200000 >;
        };

Reported-by: Mateusz Holenko <mholenko@antmicro.com>
Signed-off-by: Stafford Horne <shorne@gmail.com>

Author: stffrdhrn

arch/openrisc/kernel/setup.c

@@ -292,13 +292,15 @@ void __init setup_arch(char **cmdline_p)
 	init_mm.brk = (unsigned long)_end;
 
 #ifdef CONFIG_BLK_DEV_INITRD
-	initrd_start = (unsigned long)&__initrd_start;
-	initrd_end = (unsigned long)&__initrd_end;
 	if (initrd_start == initrd_end) {
+		printk(KERN_INFO "Initial ramdisk not found\n");
 		initrd_start = 0;
 		initrd_end = 0;
+	} else {
+		printk(KERN_INFO "Initial ramdisk at: 0x%p (%lu bytes)\n",
+		       (void *)(initrd_start), initrd_end - initrd_start);
+		initrd_below_start_ok = 1;
 	}
-	initrd_below_start_ok = 1;
 #endif
 
 	/* setup memblock allocator */

arch/openrisc/kernel/vmlinux.lds.S

@@ -96,18 +96,6 @@ SECTIONS
 
         __init_end = .;
 
-	. = ALIGN(PAGE_SIZE);
-	.initrd			: AT(ADDR(.initrd) - LOAD_OFFSET)
-	{
-		__initrd_start = .;
-		*(.initrd)
-		__initrd_end = .;
-		FILL (0);
-                . = ALIGN (PAGE_SIZE);
-	}
-
-        __vmlinux_end = .;            /* last address of the physical file */
-
 	BSS_SECTION(0, 0, 0x20)
 
         _end = .;