hwmv2: clean up arm64 soc and board empty directory

There is no legacy ARM64 SoC and Board available, so delete
the arm64 directory.

Signed-off-by: Jiafei Pan <Jiafei.Pan@nxp.com>

boards/boards_legacy/arm64/index.rst

@@ -1,10 +0,0 @@
-.. _boards-arm64:
-
-ARM64 Boards
-############
-
-.. toctree::
-   :maxdepth: 1
-   :glob:
-
-   **/index

soc/soc_legacy/arm64/CMakeLists.txt

@@ -1,7 +0,0 @@
-# SPDX-License-Identifier: Apache-2.0
-
-if(SOC_FAMILY)
-  add_subdirectory(${SOC_FAMILY})
-else()
-  add_subdirectory(${SOC_NAME})
-endif()

soc/soc_legacy/arm64/Kconfig

@@ -1,11 +0,0 @@
-# General options signifying CPU capabilities of ARM64 SoCs
-
-# Copyright (c) 2018 Nordic Semiconductor ASA.
-# SPDX-License-Identifier: Apache-2.0
-
-config SOC_PART_NUMBER
-	string
-	help
-	  This string holds the full part number of the SoC. It is a hidden option
-	  that you should not set directly. The part number selection choice defines
-	  the default value for this string.