drm/amd: Update `update_pcie_parameters` functions to use uint8_t arguments

The matching values for `pcie_gen_cap` and `pcie_width_cap` when
fetched from powerplay tables are 1 byte, so narrow the arguments
to match to ensure min() and max() comparisons without casts.

Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>