[PAC][lld] Fix reloc against adrp imm in PAC PLT header (#113429)
The PAC PLT header contains adrp instruction which immediate should be
filled. In https://reviews.llvm.org/D62609, the adrp instruction address
was calculated incorrectly. This patch resolves the issue.
The test is already present in test/ELF/aarch64-feature-pac.s