fix build with saml21, update microchip driver submodule

hw/bsp/saml21/boards/atsaml21_xpro/saml21j18b_flash.ld

@@ -135,6 +135,7 @@ SECTIONS
         . = ALIGN(4);
         _ebss = . ;
         _ezero = .;
+        end = .;
     } > ram
 
     /* stack section */

hw/mcu/microchip

@@ -1 +1 @@
-Subproject commit f7087f04783c896627061fc151fa3527b73733c7
+Subproject commit 58eb3763200ff51a998be5f537acf67299add227