stm32/boards/B_L072Z_LRWAN1: Lower default ROM level to "Core".

Re-enable some features required for the board to still build and the lora
driver to run.

This board only has 192KB of flash total, so default stm32 build is very
close to the limit.

Before:

LINK build-B_L072Z_LRWAN1/firmware.elf
   text    data     bss     dec     hex filename
 184352      68   14112  198532   30784 build-B_L072Z_LRWAN1/firmware.elf

(12256 bytes free)

After:

LINK build-B_L072Z_LRWAN1/firmware.elf
   text    data     bss     dec     hex filename
 155028      68   14052  169148   294bc build-B_L072Z_LRWAN1/firmware.elf

(41580 bytes free)

This work was funded through GitHub Sponsors.
Signed-off-by: NAngus Gratton <angus@redyak.com.au>

ports/stm32/boards/B_L072Z_LRWAN1/mpconfigboard.h

@@ -5,8 +5,13 @@
 #define MICROPY_HW_BOARD_NAME       "B-L072Z-LRWAN1"
 #define MICROPY_HW_MCU_NAME         "STM32L072CZ"
 
+#define MICROPY_CONFIG_ROM_LEVEL (MICROPY_CONFIG_ROM_LEVEL_CORE_FEATURES)
+
+#define MICROPY_HELPER_REPL         (1)
+#define MICROPY_KBD_EXCEPTION       (1)
 #define MICROPY_EMIT_THUMB          (0)
 #define MICROPY_EMIT_INLINE_THUMB   (0)
+#define MICROPY_ENABLE_SCHEDULER    (1)
 #define MICROPY_OPT_COMPUTED_GOTO   (0)
 #define MICROPY_PY_BUILTINS_COMPLEX (0)
 #define MICROPY_PY_GENERATOR_PEND_THROW (0)
@@ -18,6 +23,8 @@
 #define MICROPY_PY_STM              (0)
 #define MICROPY_PY_PYB_LEGACY       (0)
 #define MICROPY_PY_HEAPQ            (0)
+#define MICROPY_PY_OS               (1)
+#define MICROPY_PY_TIME             (1)
 
 #define MICROPY_HW_ENABLE_INTERNAL_FLASH_STORAGE (0)
 #define MICROPY_HW_ENABLE_RTC       (1)