microblaze: remove obsolete DEBUG_BOOTMEM

"git grep" shows this is the last piece of code using DEBUG_BOOTMEM,
so remove it.
Signed-off-by: WANG Cong <amwang@redhat.com>
Signed-off-by: Michal Simek <monstr@monstr.eu>

arch/microblaze/Kconfig.debug

@@ -23,8 +23,4 @@ config HEART_BEAT
 	  This option turns on/off heart beat kernel functionality.
 	  First GPIO node is taken.
 
-config DEBUG_BOOTMEM
-	depends on DEBUG_KERNEL
-	bool "Debug BOOTMEM initialization"
-
 endmenu

arch/microblaze/configs/mmu_defconfig

@@ -66,5 +66,4 @@ CONFIG_DEBUG_SPINLOCK=y
 CONFIG_DEBUG_INFO=y
 # CONFIG_RCU_CPU_STALL_DETECTOR is not set
 CONFIG_EARLY_PRINTK=y
-CONFIG_DEBUG_BOOTMEM=y
 # CONFIG_CRYPTO_ANSI_CPRNG is not set