fix(system): removed the exe flag from psram memory for esp32

extern_ram_seg segment was marked as RWX in the linker script
even though we cannot run code from PSRAM on ESP32.

This is a link-time check, and actual CPU RWX permissions are
controlled seperately so this has no practical implications,
but it could mistakenly be remarked upon during security scans
or checks by customers.

components/esp_system/ld/esp32/memory.ld.in

@@ -122,7 +122,7 @@ MEMORY
   rtc_slow_reserved_seg(RW) :        org = 0x50000000 + 0x2000 - RESERVE_RTC_MEM, len = RESERVE_RTC_MEM
 
   /* external memory */
-  extern_ram_seg(RWX)  :             org = 0x3F800000,
+  extern_ram_seg(RW)  :              org = 0x3F800000,
                                      len = 0x400000
 }