[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/cpu.cpp

@@ -11,6 +11,7 @@
 #include "log.h"
 #include "msr.h"
 #include "objects/vm_area.h"
+#include "syscall.h"
 #include "tss.h"
 
 cpu_data g_bsp_cpu_data;
@@ -98,6 +99,8 @@ init_cpu(bool bsp)
 
 		tss->ist_stack(ist) = stack_top;
 	}
+	// Set up the syscall MSRs
+	syscall_enable();
 
 	// Set up the page attributes table
 	uint64_t pat = rdmsr(msr::ia32_pat);