libc: Add Scorpion-optimized memcpy and memset

 * Optimized routines from Qualcomm for msm8660 class SoCs
 * Enable with TARGET_CPU_VARIANT := scorpion

Change-Id: I01d0f22efba5a418ddd20fca0d0c570d855e0f6f
libc: Use the fast strlen on Scorpion too

Change-Id: I9ba50a469de27269adc008c2a96767830ad6b70b