cmake: zephyr: samples: arch: Move project() after find_package(Zephyr)
It is a Zephyr build system's requirement to call project() after
find_package(Zephyr).  Follow that rule.
# SPDX-License-Identifier: Apache-2.0
-project(csp_arch)
cmake_minimum_required(VERSION 3.20)
find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+project(csp_arch)
+
target_sources(app PRIVATE main.c)
target_link_libraries(app PRIVATE libcsp)
