env: allow flash and nand env driver to compile together

Define env_ptr as static in flash and nand env driver to
allow these to compile together.

Signed-off-by: Rajesh Bhagat <rajesh.bhagat@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>

include/environment.h

@@ -157,7 +157,6 @@ extern env_t environment;
 #endif /* ENV_IS_EMBEDDED */
 
 extern const unsigned char default_environment[];
-extern env_t *env_ptr;
 
 #if defined(CONFIG_NEEDS_MANUAL_RELOC)
 extern void env_reloc(void);