ppc: Enable full relocation to RAM

The following changes allow U-Boot to fully relocate from flash to
RAM:
 - Remove linker scripts' .fixup sections from the .text section
 - Add -mrelocatable to PLATFORM_RELFLAGS for all boards
 - Define CONFIG_RELOC_FIXUP_WORKS for all boards

Previously, U-Boot would partially relocate, but statically initialized
pointers needed to be manually relocated.

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>

board/w7o/u-boot.lds

@@ -60,7 +60,6 @@ SECTIONS
     cpu/ppc4xx/start.o	(.text)
     board/w7o/init.o	(.text)
     *(.text)
-    *(.fixup)
     *(.got1)
   }
   _etext = .;

board/w7o/u-boot.lds.debug

@@ -64,7 +64,6 @@ SECTIONS
     common/env_embedded.o(.text)
 
     *(.text)
-    *(.fixup)
     *(.got1)
   }
   _etext = .;