m32r: section noise in head.S

usual "introduce .text.head, put it in front of TEXT_TEXT in vmlinux.lds.S,
make the stuff up to jump to start_kernel live in it", same as on other
targets.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>