nios2: Update linker scripts to ensure appended device tree is aligned

nios2: Update linker scripts to ensure appended device tree is aligned

With commit 0535e46d55d7 ("scripts/dtc: Update to upstream version
v1.7.2-35-g52f07dcca47c") it is now a fatal error to U-Boot if our
device tree is not 8-byte aligned. In commit 85f586035d75 ("ARM: OMAP2+:
Pad SPL binary to 8-byte alignment before DTB") Beleswar Padhi explains
that we must have ALIGN(x) statements inside of a section to ensure that
padding is included and not simply that the linker address counter is
incremented. To that end, this patch:
- Aligns the final section before _end 8-bytes by adding '. = ALIGN(8);'
  to the final section before the symbol.
- Remove a now-spurious  '. = ALIGN(x);' statement that was intended to
  provide the above alignments.
- Ensure that we do have alignment by adding an ASSERT so that when not
  aligned we fail to link (and explain why).

Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Tom Rini <trini@konsulko.com>