zephyr: Add separate Zephyr config for "minimal" build.

In anticipation of enabling more features in the default build. Also, fix
compilation of minimal build.

zephyr/Makefile

@@ -84,7 +84,7 @@ $(Z_SYSGEN_H):
 	-$(MAKE) -f Makefile.zephyr BOARD=$(BOARD) CONF_FILE=$(CONF_FILE)
 
 minimal:
-	$(MAKE) BOARD=$(BOARD) CFLAGS_EXTRA='-DMP_CONFIGFILE="<mpconfigport_minimal.h>"' FROZEN_DIR=
+	$(MAKE) BOARD=$(BOARD) CONF_FILE=prj_minimal.conf CFLAGS_EXTRA='-DMP_CONFIGFILE="<mpconfigport_minimal.h>"' FROZEN_DIR=
 
 # Clean Zephyr things too
 clean: z_clean

zephyr/mpconfigport_minimal.h

@@ -37,6 +37,7 @@
 #define MICROPY_ENABLE_GC           (1)
 #define MICROPY_HELPER_REPL         (1)
 #define MICROPY_REPL_AUTO_INDENT    (1)
+#define MICROPY_KBD_EXCEPTION       (1)
 #define MICROPY_CPYTHON_COMPAT      (0)
 #define MICROPY_PY_ASYNC_AWAIT      (0)
 #define MICROPY_PY_ATTRTUPLE        (0)

zephyr/prj_minimal.conf

+CONFIG_STDOUT_CONSOLE=y
+CONFIG_CONSOLE_HANDLER=y
+CONFIG_UART_CONSOLE_DEBUG_SERVER_HOOKS=y
+CONFIG_NEWLIB_LIBC=y
+CONFIG_FLOAT=y
+CONFIG_MAIN_STACK_SIZE=4096