tests/amdgpu: Fix various warnings (v2)

This patch fixes the following warnings:
-Wformat=
-Wmaybe-uninitialized
-Wmisleading-indentation
-Wstringop-truncation
-Wunused-function
-Wunused-variable

It also removes forward declarations and moves
global functions to the bottom, keeping locals
at the top, in ras_tests.c.

v2: Fix compilation.

Signed-off-by: Luben Tuikov <luben.tuikov@amd.com>