Fix a build error with crypto variants

There was an error that PX4_CRYPTO was cached accross variants, if it was
defined just for one variant.

This synchronizes the caching of BOARD_CRYPTO with other similar BOARD_ flags;
it is set as INTERNAL and "1" when enabled.

Also remove handling of BOARD_KEYSTORE; it is not used anywhere after
changing the crypto under src/drivers. If a separate keystore driver
is required, it is just selected as any other driver in px4board

Signed-off-by: Jukka Laitinen <jukkax@ssrc.tii.ae>

cmake/kconfig.cmake

@@ -298,14 +298,10 @@ if(EXISTS ${BOARD_DEFCONFIG})
 	endif()
 
 	if(CRYPTO)
-		set(PX4_CRYPTO ${CRYPTO} CACHE STRING "PX4 crypto implementation" FORCE)
+		set(PX4_CRYPTO "1" CACHE INTERNAL "PX4 crypto implementation" FORCE)
 		add_definitions(-DPX4_CRYPTO)
 	endif()
 
-	if(KEYSTORE)
-		set(PX4_KEYSTORE ${KEYSTORE} CACHE STRING "PX4 keystore implementation" FORCE)
-	endif()
-
 	if(LINKER_PREFIX)
 		set(PX4_BOARD_LINKER_PREFIX ${LINKER_PREFIX} CACHE STRING "PX4 board linker prefix" FORCE)
 	else()