x86,kcfi: Fix EXPORT_SYMBOL vs kCFI

The expectation is that all EXPORT'ed symbols are free to have their
address taken and called indirectly. The majority of the assembly
defined functions currently violate this expectation.

Make then all use SYM_TYPED_FUNC_START() in order to emit the proper
kCFI preamble.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Link: https://lore.kernel.org/r/20250207122546.302679189@infradead.org