staging: rtl8187se: Convert _RT_RF_POWER_STATE typedef into an enum

The Documentation/CodingStyle doesn't recommend the use of typedef,
convert this to an enum.

While at it, I have also renamed the variable names that were used in
this typedef not to use Hungarian notation.

Signed-off-by: Ana Rey <anarey@gmail.com>
Signed-off-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>