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/configs/xenguest_arm64_defconfig b/configs/xenguest_arm64_defconfig
index 45559a1..46473c2 100644
--- a/configs/xenguest_arm64_defconfig
+++ b/configs/xenguest_arm64_defconfig
@@ -14,6 +14,8 @@
 CONFIG_CMD_BOOTEFI=n
 CONFIG_CMD_BOOTEFI_HELLO_COMPILE=n
 CONFIG_CMD_ELF=n
+CONFIG_CMD_EXT4=y
+CONFIG_CMD_FAT=y
 CONFIG_CMD_GO=n
 CONFIG_CMD_RUN=n
 CONFIG_CMD_IMI=n
@@ -41,6 +43,8 @@
 CONFIG_CMD_SAVEENV=n
 CONFIG_CMD_UMS=n
 
+CONFIG_CMD_PVBLOCK=y
+
 #CONFIG_USB=n
 # CONFIG_ISO_PARTITION is not set