Build: Reorganize BL2 configuration in cmake

This commit moves the BL2 related configuration switches from the
CommonConfig.cmake file to a separate MCUBootConfig.cmake file to
make its maintenance easier.

Change-Id: I3869528bdbd2a5a071f3b3cc4b2782d22114b1ca
Signed-off-by: David Vincze <david.vincze@arm.com>
diff --git a/bl2/ext/mcuboot/CMakeLists.txt b/bl2/ext/mcuboot/CMakeLists.txt
index 3b4bf10..6f8cad8 100644
--- a/bl2/ext/mcuboot/CMakeLists.txt
+++ b/bl2/ext/mcuboot/CMakeLists.txt
@@ -129,6 +129,9 @@
 #Generate binary file from axf
 compiler_generate_binary_output(${PROJECT_NAME})
 
+message(STATUS "MCUBOOT_UPGRADE_STRATEGY is set to: '${MCUBOOT_UPGRADE_STRATEGY}'.")
+message(STATUS "MCUBOOT_SIGNATURE_TYPE is set to: '${MCUBOOT_SIGNATURE_TYPE}'.")
+
 #Set macro definitions for the project.
 target_compile_definitions(${PROJECT_NAME} PRIVATE
 							MCUBOOT_VALIDATE_SLOT0
@@ -153,7 +156,8 @@
 elseif (${MCUBOOT_UPGRADE_STRATEGY} STREQUAL "SWAP")
 	#No compile definition needs to be specified for this upgrade strategy
 else()
-	message(FATAL_ERROR "ERROR: MCUBoot supports OVERWRITE_ONLY, SWAP, NO_SWAP and RAM_LOADING upgrade strategies only.")
+	get_property(_upgrade_strategies CACHE MCUBOOT_UPGRADE_STRATEGY PROPERTY STRINGS)
+	message(FATAL_ERROR "ERROR: MCUBoot supports the ${_upgrade_strategies} upgrade strategies only.")
 endif()
 
 #Set install location. Keep original value to avoid overriding command line settings.