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

sandbox: 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 _image_binary_end (for xPL phases) by
  8-bytes by adding '. = ALIGN(8);' to the final section before the
  symbol.
- Ensure that we do have alignment by adding an ASSERT so that when not
  aligned we fail to link (and explain why).

Signed-off-by: Tom Rini <trini@konsulko.com>