FROMLIST: kbuild: fix LD_DEAD_CODE_DATA_ELIMINATION

Don't remove .head.text or .exitcall.exit when linking with --gc-sections,
and include .init.text.* in .init.text and .init.rodata.* in .init.rodata.

Bug: 62093296
Bug: 67506682
Change-Id: Ia0f9e735d04c2322dcc8bcfc94241f0551b149c4
(am from https://patchwork.kernel.org/patch/10085773/

)
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>