ARCv2: Allow enabling PAE40 w/o HIGHMEM

This allows for regression testing in PAE specific code as we lack
a 32+ bit physical memory platform other than nSIM.
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

arch/arc/Kconfig

@@ -458,7 +458,6 @@ config ARC_HAS_PAE40
 	bool "Support for the 40-bit Physical Address Extension"
 	default n
 	depends on ISA_ARCV2
-	select HIGHMEM
 	help
 	  Enable access to physical memory beyond 4G, only supported on
 	  ARC cores with 40 bit Physical Addressing support