Remove non position-independent pseudo instructions (ldr rx,=label)

This commit fixes the issue #83.

Approach 1: (for NE10_fft_float32.neon.s, NE10_fft_float32.neonv8.S, NE10_fft_int16.neon.s)
- Use "adr" pseudo instruction

Approach 2: (for NE10_fir.neon.s, NE10_iir.neon.s)
- Use GOT based access