e-hal: Only perform aligned writes to Epiphany SRAM

This implements a wrapper around libc/gcc memcpy() which ensures that
only aligned accesses are performed.

The Epiphany chip is configured as device memory. As such it does not
have to support unaligned access. In fact the ARM MMU will issue TRAP
exceptions for some instructions that perform unaligned access to device
memory.

* src/e-hal/src/epiphany-hal.c (static inline void *aligned_memcpy):
Implemented wrapper that only calls memcpy when src dst and size
are 32 bit WORD aligned.
(ssize_t ee_write_buf): Use aligned_memcpy() instead of memcpy().