Initialize the stack pointer to allow rPi to jump into C.

The stack pointer is set up so that it uses the space below our .text
section at 0x8000. The stack pointer actually points at one entry less
than the specified address, so it starts at 0x8000 - sizeof(uint32) and
grows downwards from there.

src/system/boot/platform/raspberrypi_arm/entry.S

@@ -19,6 +19,10 @@ jmp_loader:
 	bx r12
 	*/
 
+	/* Setup initial stack right below our .text section (growing downwards
+		into the space reserved for .init) */
+	mov sp, #0x8000
+
 	b _start
 
 	/* Cause exception if loader returns */