cpufreq: amd-pstate: auto-load pstate driver by default

If the `amd-pstate` driver is not loaded automatically by default,
it is because the kernel command line parameter has not been added.
To resolve this issue, it is necessary to call the `amd_pstate_set_driver()`
function to enable the desired mode (passive/active/guided) before registering
the driver instance.

This ensures that the driver is loaded correctly without relying on the kernel
command line parameter.

When there is no parameter added to command line, Kernel config will
provide the default mode to load.

Meanwhile, user can add driver mode in command line which will override
the kernel config default option.

Reported-by: Andrei Amuraritei <andamu@posteo.net>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218705


Signed-off-by: Perry Yuan <perry.yuan@amd.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Link: https://lore.kernel.org/r/83301c4cea4f92fb19e14b23f2bac7facfd8bdbb.1718811234.git.perry.yuan@amd.com


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