Refine GPU discovery to bootstrap once

Now that we call the GPU discovery routines many times to
update memory, this splits initial discovery from free memory
updating.

gpu/cpu_common.go

@@ -1,21 +1,20 @@
 package gpu
 
 import (
-	"log/slog"
-
 	"golang.org/x/sys/cpu"
 )
 
 func GetCPUVariant() string {
+	return getCPUCapability().ToVariant()
+}
+
+func getCPUCapability() CPUCapability {
 	if cpu.X86.HasAVX2 {
-		slog.Debug("CPU has AVX2")
-		return "avx2"
+		return CPUCapabilityAVX2
 	}
 	if cpu.X86.HasAVX {
-		slog.Debug("CPU has AVX")
-		return "avx"
+		return CPUCapabilityAVX
 	}
-	slog.Debug("CPU does not have vector extensions")
 	// else LCD
-	return ""
+	return CPUCapabilityBase
 }