upm_platform: use __linux__ define to detect linux platforms
upm_platform: use __linux__ define to detect linux platforms

Signed-off-by: Jon Trulson <08664b19c2d4086eb239dd8ec32d593676a5b9e4@ics.com>

sasmita/upm,intel-iot-devkit/upm,stefan-andritoiu/upm,Jon-ICS/upm,stefan-andritoiu/upm,Jon-ICS/upm,spitfire88/upm,nitirohilla/upm,Jon-ICS/upm,malikabhi05/upm,g-vidal/upm,stefan-andritoiu/upm,pylbert/upm,g-vidal/upm,Propanu/upm,Propanu/upm,sasmita/upm,stefan-andritoiu/upm,malikabhi05/upm,Jon-ICS/upm,pylbert/upm,sasmita/upm,spitfire88/upm,malikabhi05/upm,g-vidal/upm,pylbert/upm,whbruce/upm,nitirohilla/upm,nitirohilla/upm,nitirohilla/upm,intel-iot-devkit/upm,skiselev/upm,stefan-andritoiu/upm,malikabhi05/upm,nitirohilla/upm,jontrulson/upm,pylbert/upm,intel-iot-devkit/upm,g-vidal/upm,Propanu/upm,whbruce/upm,skiselev/upm,skiselev/upm,jontrulson/upm,g-vidal/upm,skiselev/upm,pylbert/upm,pylbert/upm,sasmita/upm,intel-iot-devkit/upm,Jon-ICS/upm,skiselev/upm,spitfire88/upm,Propanu/upm,Propanu/upm,spitfire88/upm,jontrulson/upm,whbruce/upm,intel-iot-devkit/upm,skiselev/upm,Propanu/upm,stefan-andritoiu/upm,sasmita/upm,malikabhi05/upm,jontrulson/upm,jontrulson/upm,whbruce/upm,whbruce/upm,spitfire88/upm,intel-iot-devkit/upm,malikabhi05/upm,g-vidal/upm