timekeeper sources: add an option to disable each one of them

kernel-src/arch/x86-64/hpet.c

@@ -5,6 +5,7 @@
 #include <kernel/vmm.h>
 #include <kernel/interrupt.h>
 #include <arch/tsc.h>
+#include <kernel/cmdline.h>
 
 #include <uacpi/acpi.h>
 #include <uacpi/tables.h>
@@ -62,6 +63,9 @@ static void counterirq(isr_t *isr, context_t *context) {
 }
 
 static bool hpet_probe(void) {
+	if (cmdline_get("nohpet"))
+		return false;
+
 	bool usable = false;
 	struct acpi_hpet *table;
 	uacpi_table tbl;

kernel-src/arch/x86-64/kvmclock.c

@@ -6,6 +6,7 @@
 #include <arch/cpuid.h>
 #include <kernel/pmm.h>
 #include <arch/tsc.h>
+#include <kernel/cmdline.h>
 
 #define KVM_TIMER_SYSTEM_TIME_ALIGNMENT 4
 #define KVM_TIMER_SYSTEM_TIME_ENABLE 1
@@ -23,6 +24,9 @@ typedef struct {
 } __attribute__((packed)) kvm_timer_info_t;
 
 static bool kvm_timer_probe(void) {
+	if (cmdline_get("nokvmclock"))
+		return false;
+
 	// figure out if we are running in kvm
 	uint32_t base = cpuid_find_hypervisor_base_kvm();
 	if (base == 0)

kernel-src/arch/x86-64/tsc.c

@@ -3,8 +3,13 @@
 #include <arch/cpuid.h>
 #include <logging.h>
 #include <kernel/alloc.h>
+#include <arch/hpet.h>
+#include <kernel/cmdline.h>
 
 static bool tsc_probe(void) {
+	if (cmdline_get("notsc"))
+		return false;
+
 	cpuid_results_t cpuid_results;
 
 	uint32_t max_extended_leaf = cpuid_extended_max_leaf();