[kernel] Update syscall MSRs for all CPUs

Since SYSCALL/SYSRET rely on MSRs to control their function, split out
syscall_enable() into syscall_initialize() and syscall_enable(), the
latter being called on all CPUs. This affects not just syscalls but also
the kernel_to_user_trampoline.

Additionally, do away with the max syscalls, and just make a single page
of syscall pointers and name pointers. Max syscalls was fragile and
needed to be kept in sync in multiple places.

src/kernel/main.cpp

@@ -149,6 +149,7 @@ kernel_main(args::header *header)
 		}
 	}
 
+	syscall_initialize();
 
 	device_manager &devices = device_manager::get();
 	devices.parse_acpi(header->acpi_table);
@@ -184,7 +185,6 @@ kernel_main(args::header *header)
 	}
 	*/
 
-	syscall_enable();
 	scheduler *sched = new scheduler(devices.get_lapic());
 
 	// Skip program 0, which is the kernel itself