drm/xe/guc: Add SLPC power profile interface

drm/xe/guc: Add SLPC power profile interface

GuC has an interface to set a power profile for the SLPC algorithm.
Base mode is default and ensures a balanced performance, power_saving
mode has conservative up/down thresholds and is suitable for use with
apps that typically need to be power efficient. This will result in
lower GT frequencies, thus consuming lower power.

Selected power profile will be displayed in this format:

$ cat power_profile

  [base]    power_saving

$ echo power_saving > power_profile
$ cat power_profile

  base    [power_saving]

v2: Address review comments (Rodrigo)

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://lore.kernel.org/r/20250903232120.390190-1-vinay.belgaumkar@intel.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>