board: Introduce xenguest_arm64 board

Introduce a minimal Xen guest board running as a virtual
machine under Xen Project's hypervisor [1], [2].

Part of the code is ported from Xen mini-os and also uses
work initially done by different authors from NXP: please see
relevant files for their copyrights.

[1] https://xenbits.xen.org
[2] https://wiki.xenproject.org/

Signed-off-by: Andrii Anisov <andrii_anisov@epam.com>
Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Signed-off-by: Anastasiia Lukianenko <anastasiia_lukianenko@epam.com>

configs/xenguest_arm64_defconfig

@@ -0,0 +1,56 @@
+CONFIG_ARM=y
+CONFIG_POSITION_INDEPENDENT=y
+CONFIG_SYS_TEXT_BASE=0x40080000
+CONFIG_SYS_MALLOC_F_LEN=0x2000
+CONFIG_IDENT_STRING=" xenguest"
+CONFIG_TARGET_XENGUEST_ARM64=y
+CONFIG_BOOTDELAY=10
+
+CONFIG_SYS_PROMPT="xenguest# "
+
+CONFIG_CMD_NET=n
+CONFIG_CMD_BDI=n
+CONFIG_CMD_BOOTD=n
+CONFIG_CMD_BOOTEFI=n
+CONFIG_CMD_BOOTEFI_HELLO_COMPILE=n
+CONFIG_CMD_ELF=n
+CONFIG_CMD_GO=n
+CONFIG_CMD_RUN=n
+CONFIG_CMD_IMI=n
+CONFIG_CMD_IMLS=n
+CONFIG_CMD_XIMG=n
+CONFIG_CMD_EXPORTENV=n
+CONFIG_CMD_IMPORTENV=n
+CONFIG_CMD_EDITENV=n
+CONFIG_CMD_ENV_EXISTS=n
+CONFIG_CMD_MEMORY=y
+CONFIG_CMD_CRC32=n
+CONFIG_CMD_DM=n
+CONFIG_CMD_LOADB=n
+CONFIG_CMD_LOADS=n
+CONFIG_CMD_FLASH=n
+CONFIG_CMD_GPT=n
+CONFIG_CMD_FPGA=n
+CONFIG_CMD_ECHO=n
+CONFIG_CMD_ITEST=n
+CONFIG_CMD_SOURCE=n
+CONFIG_CMD_SETEXPR=n
+CONFIG_CMD_MISC=n
+CONFIG_CMD_UNZIP=n
+CONFIG_CMD_LZMADEC=n
+CONFIG_CMD_SAVEENV=n
+CONFIG_CMD_UMS=n
+
+#CONFIG_USB=n
+# CONFIG_ISO_PARTITION is not set
+
+#CONFIG_EFI_PARTITION=y
+# CONFIG_EFI_LOADER is not set
+
+CONFIG_DM=y
+# CONFIG_MMC is not set
+# CONFIG_DM_SERIAL is not set
+# CONFIG_REQUIRE_SERIAL_CONSOLE is not set
+
+CONFIG_OF_BOARD=y
+CONFIG_OF_LIBFDT=y