disk: add partition type helpers

Add helper methods on `Partition` so that we can easily "detect" if
they are of the type BIOS-BOOT or PReP. Add the PReP GUID for GPT
as well.

internal/disk/disk.go

@@ -41,6 +41,8 @@ const (
 	EFISystemPartitionUUID = "68B2905B-DF3E-4FB3-80FA-49D1E773AA33"
 	EFIFilesystemUUID      = "7B77-95E7"
 
+	PRePartitionGUID = "9E1A2D38-C612-4316-AA26-8B49521E5A8B"
+
 	RootPartitionUUID = "6264D520-3FB9-423F-8AB8-7A0A8E3D3562"
 )
 

internal/disk/partition.go

@@ -69,3 +69,19 @@ func (p *Partition) EnsureSize(s uint64) bool {
 	}
 	return false
 }
+
+func (p *Partition) IsBIOSBoot() bool {
+	if p == nil {
+		return false
+	}
+
+	return p.Type == BIOSBootPartitionGUID
+}
+
+func (p *Partition) IsPReP() bool {
+	if p == nil {
+		return false
+	}
+
+	return p.Type == "41" || p.Type == PRePartitionGUID
+}