libfdt: replace ARCH_FIXUP_FDT with ARCH_FIXUP_FDT_MEMORY

Commit e2f88dfd2d ("libfdt: Introduce new ARCH_FIXUP_FDT option")
allows us to skip memory setup of DTB, but a problem for ARM is that
spin_table_update_dt() and psci_update_dt() are skipped as well if
CONFIG_ARCH_FIXUP_FDT is disabled.

This commit allows us to skip only fdt_fixup_memory_banks() instead
of the whole of arch_fixup_fdt().  It will be useful when we want to
use a memory node from a kernel DTB as is, but need some fixups for
Spin-Table/PSCI.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Alexey Brodkin <abrodkin@synopsys.com>
Acked-by: Simon Glass <sjg@chromium.org>
Fixed build error for x86:
Signed-off-by: Simon Glass <sjg@chromium.org>

common/fdt_support.c

@@ -381,6 +381,7 @@ void do_fixup_by_compat_u32(void *fdt, const char *compat,
 	do_fixup_by_compat(fdt, compat, prop, &tmp, 4, create);
 }
 
+#ifdef CONFIG_ARCH_FIXUP_FDT_MEMORY
 /*
  * fdt_pack_reg - pack address and size array into the "reg"-suitable stream
  */
@@ -459,6 +460,7 @@ int fdt_fixup_memory_banks(void *blob, u64 start[], u64 size[], int banks)
 	}
 	return 0;
 }
+#endif
 
 int fdt_fixup_memory(void *blob, u64 start, u64 size)
 {