[ELF/AArch64] Fix overflow checks for R_AARCH64_{ABS,PREL}{16,32} relocations.

ABI specifies the allowed range for these relocations as 2^(n-1) <= X < 2^n.

The patch fixes checks and introduces precise tests for these relocations.

Differential revision: http://reviews.llvm.org/D14957

llvm-svn: 254146