sh: switch to NO_BOOTMEM

Commit 0fa1c579 ("of/fdt: use memblock_virt_alloc for early alloc")
inadvertently switched the DT unflattening allocations from memblock to
bootmem which doesn't work because the unflattening happens before
bootmem is initialized. Swapping the order of bootmem init and
unflattening could also fix this, but removing bootmem is desired. So
enable NO_BOOTMEM on SH like other architectures have done.

Fixes: 0fa1c579

 ("of/fdt: use memblock_virt_alloc for early alloc")
Reported-by: Rich Felker <dalias@libc.org>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Rich Felker <dalias@libc.org>