i#1551 port to ARM: implement _start

Implements _start for -early early injection support on ARM.
Fix style violations
Fix noisy encoding log by making DOLOG match the level of interior logs.
i#1551 port to ARM: implement (naive) memcpy and memset

We need our own memcpy and memset to avoid pulling in libc's version.
We have optimized x86 versions in x86.asm.
This commit adds initial naive unoptimized ARM versions.

Also fixes a bug in the ARM safe_read_asm.