alpha: beautify vmlinux.lds

Introduced a consistent style in vmlinux.lds and it now matches the
soon-to-be common style for all arch's vmlinux.lds files.

In addition:
- Replaced hardcoded constant with PAGE_SIZE
- Fix page.h so PAGE_SIZE can be used from assembler and in lds files
- Move a few labels inside brackets so linker alignment will not
  make label point ot a too low address
- Replaced DWARF and STABS sections with definitions from asm-generic

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Richard Henderson <rth@twiddle.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>