m68k: Enable dead code elimination

Allow the experimental dead code elimination config to be enabled.

For my 68000 nommu config this frees up a few hundred K of memory
so seems worth while.

Boot and build tested on nommu and mmu enabled configs.

Before:
Memory: 5388K/8192K available (1986K kernel code, 114K rwdata,
244K rodata, 92K init, 41K bss, 2624K reserved, 0K cma-reserved)

After
Memory: 5684K/8192K available (1714K kernel code, 112K rwdata,
228K rodata, 92K init, 37K bss, 2328K reserved, 0K cma-reserved)

Signed-off-by: Daniel Palmer <[e-mail]>
Acked-by: Greg Ungerer <[e-mail]>
Tested-by: Finn Thain <[e-mail]>
Reviewed-by: Geert Uytterhoeven <[e-mail]>
Link: https://lore.kernel.org/[e-mail]
Signed-off-by: Geert Uytterhoeven <[e-mail]>

arch/m68k/Kconfig

···
 	select HAVE_ASM_MODVERSIONS
 	select HAVE_DEBUG_BUGVERBOSE
 	select HAVE_EFFICIENT_UNALIGNED_ACCESS if !CPU_HAS_NO_UNALIGNED
+	select HAVE_LD_DEAD_CODE_DATA_ELIMINATION
 	select HAVE_MOD_ARCH_SPECIFIC
 	select HAVE_UID16
 	select MMU_GATHER_NO_RANGE if MMU