Added previous OpenCL changes for AMD, nowarp kernels

Added the modified reduce functions also for AMD and nowarp kernels.
For AMD, the following results were obtained:
- FirePro W5100(Windows): the kernel execution time dropped from (36ms,
42ms, 64ms) to (22ms, 34ms, 56ms) as reported in md.log
- For R9-290 OC: the main kernel execution time dropped from 5.6ms to
4.2ms