sunxi: Add default environment size

On boards that defines ENV_IS_NOWHERE, such as the NES classic, commit
19dbe7d1a3f7 ("common: Move environment choice to Kconfig") broke the build
because of a missing environment size.

Reintroduce a default environment size consistent with what we had before.
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>

include/configs/sunxi-common.h

@@ -142,6 +142,8 @@
 #if defined(CONFIG_ENV_IS_IN_MMC)
 #define CONFIG_SYS_MMC_ENV_DEV		0	/* first detected MMC controller */
 #define CONFIG_SYS_MMC_MAX_DEVICE	4
+#elif defined(CONFIG_ENV_IS_NOWHERE)
+#define CONFIG_ENV_SIZE			(128 << 10)
 #endif
 
 /* 64MB of malloc() pool */