ARM: allow DEBUG_UNCOMPRESS for omap2plus

DEBUG_UNCOMPRESS was previously disallowed for omap2plus due to
omap2plus.S's use of .data, which is not allowed in the decompressor.
Solve this by placing that data into .text when building the file into
the decompressor. This relies on .text actually being writable in the
decompressor, which it is in practice.

Cc: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Stephen Warren <swarren@nvidia.com>
---
Note that I have build-tested this with omap2plus_defconfig, but not
run-time tested it in any way.