drm/amd: Fix UBSAN array-index-out-of-bounds for Polaris and Tonga

[ Upstream commit 0f0e59075b5c22f1e871fbd508d6e4f495048356 ]

For pptable structs that use flexible array sizes, use flexible arrays.

Link: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2036742


Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>