asm-generic/vmlinux.lds.h: Fix up RW_DATA_SECTION definition.

RW_DATA_SECTION is defined to take 4 different alignment parameters,
while NOSAVE_DATA currently uses a fixed PAGE_SIZE alignment as noted
in the comments.

There are presently no in-tree users of this at present, and I just
stumbled across this while implementing the simplified script on a new
architecture port, which subsequently resulted in a syntax error.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>