xtensa: let platform override KERNELOFFSET

The linker script should not assume a fix offset in memory for the
kernel, this is platform-specific, so let the platform set it.
Signed-off-by: Johannes Weiner <jw@emlix.com>
Signed-off-by: Chris Zankel <chris@zankel.net>

arch/xtensa/kernel/vmlinux.lds.S

@@ -17,6 +17,7 @@
 #include <asm-generic/vmlinux.lds.h>
 
 #include <variant/core.h>
+#include <platform/hardware.h>
 OUTPUT_ARCH(xtensa)
 ENTRY(_start)
 
@@ -26,7 +27,9 @@ jiffies = jiffies_64 + 4;
 jiffies = jiffies_64;
 #endif
 
+#ifndef KERNELOFFSET
 #define KERNELOFFSET 0xd0001000
+#endif
 
 /* Note: In the following macros, it would be nice to specify only the
    vector name and section kind and construct "sym" and "section" using