Build: Combine compile time MCUBoot switches

Remove multiple compile time MCUBoot switches and combine their
functionality into the 'MCUBOOT_UPGRADE_STRATEGY' switch.

Change-Id: Ibed68983ca0e2ed3c291d56514e8ad93ac0dbeba
Signed-off-by: David Vincze <david.vincze@arm.com>
diff --git a/platform/ext/Mps2AN521.cmake b/platform/ext/Mps2AN521.cmake
index 80fe871..413bb1c 100644
--- a/platform/ext/Mps2AN521.cmake
+++ b/platform/ext/Mps2AN521.cmake
@@ -39,6 +39,9 @@
 
 if (BL2)
   set (BL2_LINKER_CONFIG ${BL2_SCATTER_FILE_NAME})
+  if (${MCUBOOT_UPGRADE_STRATEGY} STREQUAL "RAM_LOADING")
+      message(FATAL_ERROR "ERROR: RAM_LOADING upgrade strategy is not supported on target '${TARGET_PLATFORM}'.")
+  endif()
 endif()
 
 embedded_include_directories(PATH "${PLATFORM_DIR}/cmsis" ABSOLUTE)
@@ -167,10 +170,6 @@
   embedded_include_directories(PATH "${PLATFORM_DIR}/target/mps2/an521/cmsis_drivers" ABSOLUTE)
 endif()
 
-if (MCUBOOT_RAM_LOADING)
-	message (FATAL_ERROR "MCUBOOT_RAM_LOADING is not supported on " ${TARGET_PLATFORM})
-endif()
-
 if (NOT DEFINED BUILD_BOOT_SEED)
   message(FATAL_ERROR "Configuration variable BUILD_BOOT_SEED (true|false) is undefined!")
 elseif(BUILD_BOOT_SEED)