cpufreq/amd-pstate: Convert all perf values to u8

All perf values are always within 0-255 range, hence convert their
datatype to u8 everywhere.

Signed-off-by: Dhananjay Ugwekar <dhananjay.ugwekar@amd.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
Link: https://lore.kernel.org/r/20250205112523.201101-7-dhananjay.ugwekar@amd.com


Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>