bfd/elfnn-aarch64.c: Fix calculation of DT_RELASZ

The current code subtracts the size of the output section containing
relplt from RELASZ. In some cases this will be the same output
section as the dynamic relocs causing a value of zero to be output.
Calculating the size from input sections seems to make more sense.

bfd/ChangeLog:

2014-03-25  Will Newton  <will.newton@linaro.org>

	 * elfnn-aarch64.c (elfNN_aarch64_finish_dynamic_sections):
	 Set value of DT_PLTRELSZ and DT_RELASZ based on the size
	 of input sections rather than output sections.

ld/testsuite/ChangeLog:

2014-03-25  Will Newton  <will.newton@linaro.org>

	 * ld-aarch64/aarch64-elf.exp: Add relasz dump test.
	 * ld-aarch64/relasz.d: New file.
	 * ld-aarch64/relasz.s: Likewise.