xen: pvblock: Add initial support for para-virtualized block driver

Add initial infrastructure for Xen para-virtualized block device.
This includes compile-time configuration and the skeleton for
the future driver implementation.
Add new class UCLASS_PVBLOCK which is going to be a parent for
virtual block devices.
Add new interface type IF_TYPE_PVBLOCK.

Implement basic driver setup by reading XenStore configuration.

Signed-off-by: Andrii Anisov <andrii_anisov@epam.com>
Signed-off-by: Anastasiia Lukianenko <anastasiia_lukianenko@epam.com>
Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
diff --git a/disk/part.c b/disk/part.c
index f6a3102..b69fd34 100644
--- a/disk/part.c
+++ b/disk/part.c
@@ -149,6 +149,7 @@
 	case IF_TYPE_MMC:
 	case IF_TYPE_USB:
 	case IF_TYPE_NVME:
+	case IF_TYPE_PVBLOCK:
 		printf ("Vendor: %s Rev: %s Prod: %s\n",
 			dev_desc->vendor,
 			dev_desc->revision,
@@ -288,6 +289,9 @@
 	case IF_TYPE_NVME:
 		puts ("NVMe");
 		break;
+	case IF_TYPE_PVBLOCK:
+		puts("PV BLOCK");
+		break;
 	case IF_TYPE_VIRTIO:
 		puts("VirtIO");
 		break;