mpc83xx: extend CONFIG_SYS_BOOTMAPSZ increase to mpc8308_p1m

continuation of commit 39da1ba923d55f316f9f1bb3a960e4ed91dc17ac:
"e300: increase CONFIG_SYS_BOOTMAPSZ to allow booting large kernels"

Signed-off-by: Kim Phillips <kim.phillips@freescale.com>

include/configs/mpc8308_p1m.h

@@ -437,7 +437,7 @@
  * have to be in the first 8 MB of memory, since this is
  * the maximum mapped by the Linux kernel during initialization.
  */
-#define CONFIG_SYS_BOOTMAPSZ	(8 << 20) /* Initial Memory map for Linux */
+#define CONFIG_SYS_BOOTMAPSZ	(256 << 20) /* Initial Memory map for Linux */
 
 /*
  * Core HID Setup