powerpc/8xx: Fixing issue with CONFIG_PIN_TLB

Activating CONFIG_PIN_TLB is supposed to pin the IMMR and the first
three 8Mbytes pages.  But the setting of MD_CTR to a pinnable entry was
missing before the pinning of the third 8Mb page.  As the index is
decremented module 28 (MD_RSV4D is set) after every DTLB update, the
third 8Mbytes page was not pinned.
Signed-off-by: NChristophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: NScott Wood <scottwood@freescale.com>

arch/powerpc/kernel/head_8xx.S

@@ -858,6 +858,9 @@ initial_mmu:
 	addis	r11, r11, 0x0080	/* Add 8M */
 	mtspr	SPRN_MD_RPN, r11
 
+	addi	r10, r10, 0x0100
+	mtspr	SPRN_MD_CTR, r10
+
 	addis	r8, r8, 0x0080		/* Add 8M */
 	mtspr	SPRN_MD_EPN, r8
 	mtspr	SPRN_MD_TWC, r9