drm/amdgpu: Replace remaining 1-element array with flex-array

One-element arrays are deprecated, and we are replacing them with
flexible array members instead. So, replace one-element array with
flexible-array member in struct GOP_VBIOS_CONTENT and refactor the
rest of the code accordingly.

Important to mention is that doing a build before/after this patch
results in no functional binary output differences.

This helps with the ongoing efforts to tighten the FORTIFY_SOURCE
routines on memcpy() and help us make progress towards globally
enabling -fstrict-flex-arrays=3 [1].

Link: https://github.com/KSPP/linux/issues/79
Link: https://github.com/KSPP/linux/issues/238
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101836 [1]
Signed-off-by: Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/include/atombios.h

@@ -9292,7 +9292,7 @@ typedef struct {
 
 typedef struct {
   VFCT_IMAGE_HEADER   VbiosHeader;
-  UCHAR   VbiosContent[1];
+  UCHAR   VbiosContent[];
 }GOP_VBIOS_CONTENT;
 
 typedef struct {