[cpu] Split cpuid validation into separate lib

In order to allow the bootloader to do preliminary CPUID validation
while UEFI is still handling displaying information to the user, split
most of the kernel's CPUID handling into a library to be used by both
kernel and boot.

src/kernel/main.cpp

@@ -135,8 +135,7 @@ kernel_main(args::header *header)
 	run_constructors();
 	memory_initialize_post_ctors(header);
 
-	cpu_id cpu;
-	cpu.validate();
+	cpu_validate();
 
 	for (size_t i = 0; i < header->num_modules; ++i) {
 		args::module &mod = header->modules[i];