[DO NOT MERGE] x86/kexec: Add CFI type information to relocate_kernel()

[DO NOT MERGE] x86/kexec: Add CFI type information to relocate_kernel()

A previous commit added __nocfi to machine_kexec() because it makes an
indirect call to relocate_kernel() which lacked CFI type information,
and caused the system to crash.

Use SYM_TYPED_FUNC_START() to ensure that the type information is
present, and remove the __nocfi tag.

I still can't make objtool happy with this in both GCC and Clang builds
at the same time, so not yet for merging; only included in this series
to nerd-snipe the objtool maintainers.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>