drm/radeon: fix pptable.h portability

The following isn't compatible with gcc 2.x:

pragma pack(push, 1)
...
pragma pack(pop)

replace with:

pragma pack(1)
...
pragma pack()

bug:
https://bugzilla.kernel.org/show_bug.cgi?id=67961



Signed-off-by: Alex Deucher <alexander.deucher@amd.com>