x86/kexec: Add CFI type information to relocate_kernel()

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. And emit the *actual* type
signature (0x19835999) because by default, asm code uses the type
signature emitted by the *caller*, which is never going to differ!

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