Makefile tweaks

- Force ARCH to arm;
    this allows making configs without manually setting ARCH variable
- Do not use -Os global
- Do not use -mno-unaligned-access;
    this is only for TouchWiz ROMs
- Add -funroll-loops;
    this is known to improve performance
defconfig tweaks

- Enable SCHED_AUTOGROUP;
    this dramatically improves multi-tasking performance
- Disable MSM_CACHE_ERP;
    Qualcomm recommends us to disable this on production builds
- Enable UACCESS_WITH_MEMCPY;
    this improves performance on memcpy function
- Enable STRIP_ASM_SYMS;
    this makes zImage smaller
- Disable FRAME_POINTER, enable ARM_UNWIND;
    ARM_UNWIND is generally known to be faster than FRAME_POINTER
- Disable FTRACE;
    we don't use FTRACE debugging, disabling this make the kernel lighter