samd/mcu: Use lf2s for SAMD51 and lfs1 for SAMD21.

Using lfs1 gives a smaller code, but lfs2 has more features.

ports/samd/mcu/samd21/mpconfigmcu.h

@@ -6,6 +6,7 @@
 // MicroPython emitters
 #define MICROPY_EMIT_THUMB              (0)
 #define MICROPY_EMIT_INLINE_THUMB       (0)
+#define MICROPY_MODULE_BUILTIN_INIT     (1)
 
 #define MICROPY_FLOAT_IMPL              (MICROPY_FLOAT_IMPL_FLOAT)
 #define MICROPY_PY_BUILTINS_COMPLEX     (0)

ports/samd/mcu/samd51/mpconfigmcu.mk

@@ -1,3 +1,5 @@
+MICROPY_VFS_LFS2 ?= 1
+
 SRC_S += shared/runtime/gchelper_m3.s
 
 SRC_MOD +=  $(addprefix lib/libm/,\

ports/samd/modules/_boot.py

@@ -6,11 +6,13 @@ samd.Flash.flash_init()
 bdev = samd.Flash()
 
 # Try to mount the filesystem, and format the flash if it doesn't exist.
+fs_type = uos.VfsLfs2 if hasattr(uos, "VfsLfs2") else uos.VfsLfs1
+
 try:
-    vfs = uos.VfsLfs1(bdev)
+    vfs = fs_type(bdev)
 except:
-    uos.VfsLfs1.mkfs(bdev)
-    vfs = uos.VfsLfs1(bdev)
+    fs_type.mkfs(bdev)
+    vfs = fs_type(bdev)
 uos.mount(vfs, "/")
 
 gc.collect()