Kernel/LibC: support RDTSCP based clock_gettime

RDTSCP seems to be faster than LSL and it removes the need for getting
the current cpu twice to make sure TSC is read on the correct CPU

kernel/include/kernel/API/SharedPage.h

@@ -8,6 +8,7 @@ namespace Kernel::API
 	enum SharedPageFeature : uint32_t
 	{
 		SPF_GETTIME = 1 << 0,
+		SPF_RDTSCP  = 1 << 1,
 	};
 
 	struct SharedPage

kernel/include/kernel/CPUID.h

@@ -82,6 +82,7 @@ namespace CPUID
 	bool has_pat();
 	bool has_1gib_pages();
 	bool has_invariant_tsc();
+	bool has_rdtscp();
 	uint64_t get_tsc_frequency();
 	bool has_kvm_pvclock();