x86/hvm: Use __initdata_cf_clobber for hvm_funcs

x86/hvm: Use __initdata_cf_clobber for hvm_funcs

Now that all calls through hvm_funcs are fully altcall'd, harden all the svm
and vmx function pointer targets.  This drops 106 endbr64 instructions.

Clobbering does come with a theoretical risk.  The non-pointer fields of
{svm,vmx}_function_table can in theory happen to form a bit pattern matching a
pointer into .text at a legal endbr64 instruction, but this is expected to be
implausible for anything liable to pass code review.

While at it, move hvm_funcs into __ro_after_init now that this exists.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>