[ELF] Merge relaIplt into relaDyn

`relaIplt` was added so that IRELATIVE relocations are placed at the end
of .rela.dyn (since https://reviews.llvm.org/D65651) or .rela.plt
(--pack-dyn-relocs=android[+relr]). Unfortunately, handling `relaIplt`
requires special cases all over the code base. We can extend
partitionRels/computeRels to partition both RELATIVE and IRELATIVE
relocations, rendering `relaIplt` unneeded.

The change allows IRELATIVE relocations in the DT_ANDROID_REL[A] table
(untested?!), which may be processed before other types of relocations.
This seems acceptable for Bionic's DEFINE_IFUNC_FOR use cases.

In addition, this change simplies changing .rel[a].dyn to a compact
relocation format (CREL).

SHF_INFO_LINK is removed from .rel[a].dyn with IRELATIVE relocations.
(See https://reviews.llvm.org/D89828).