[lld][ARM] Add support for 16-bit thumb group relocations

This adds support for the following relocations:
 * R_ARM_THM_ALU_ABS_G0_NC
 * R_ARM_THM_ALU_ABS_G1_NC
 * R_ARM_THM_ALU_ABS_G2_NC
 * R_ARM_THM_ALU_ABS_G3
as defined in:
https://github.com/ARM-software/abi-aa/blob/main/aaelf32/aaelf32.rst#5615static-thumb16-relocations

Differential Revision: https://reviews.llvm.org/D153407