PATCH BFD section load page support

[Timothy Wall]

The linker manipulates sections based on the load page.  It would be
rather difficult to conditionally handle load page directives in linker
scripts only if the output type is a variation of TI COFF.

Putting the load page in a coff-specific structure means the linker now
has to check the bfd output type before applying a script directive.

If you can indicate how the linker can process the load page directive
and cleanly use coff_section_tdata, please let me know your suggestions.

Tim Wall