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>

common/board_r.c

@@ -49,6 +49,7 @@
 #include <nand.h>
 #include <of_live.h>
 #include <onenand_uboot.h>
+#include <pvblock.h>
 #include <scsi.h>
 #include <serial.h>
 #include <status_led.h>
@@ -475,6 +476,16 @@ static int initr_xen(void)
 	return 0;
 }
 #endif
+
+#ifdef CONFIG_PVBLOCK
+static int initr_pvblock(void)
+{
+	puts("PVBLOCK: ");
+	pvblock_init();
+	return 0;
+}
+#endif
+
 /*
  * Tell if it's OK to load the environment early in boot.
  *
@@ -774,6 +785,9 @@ static init_fnc_t init_sequence_r[] = {
 #endif
 #ifdef CONFIG_XEN
 	initr_xen,
+#endif
+#ifdef CONFIG_PVBLOCK
+	initr_pvblock,
 #endif
 	initr_env,
 #ifdef CONFIG_SYS_BOOTPARAMS_LEN