headers: Unbreak some ARM syscalls

Restore the outside-kernel exclusion for some syscalls that was
removed by change I959b64280e184655ef8c713aa79f9e23cb1f7df4,
since these syscalls are used elsewhere.

Change-Id: I5b5bf3d78edd137e820d25281a375966b6c009ec
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