sparc64: fix alignment bug in linker definition script

The RO_DATA section were hardcoded to a specific
alignment in include/asm-generic/vmlinux.h.
But for sparc64 this did not match the PAGE_SIZE.

Introduce a new section definition named:
RO_DATA that takes actual alignment as parameter.
RODATA are provided for backward compatibility.

On top of this avoid hardcoding alignment for
sparc64 in reset of the script
Fix is build-tested on sparc64 + x86_64.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>