powerpc/8xx: use the fixmapped IMMR in cpm_reset()

Since commit f86ef74e ("powerpc/8xx: Fix vaddr for IMMR early
remap"), the IMMR area has been mapped at startup with fixmap.

Use that fixmap directly instead of calling ioremap(), this
avoids calling ioremap() early before the slab is available.
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/f816ccdbd15b97cf43c5a8c7cc8dfa8db58ff036.1568294935.git.christophe.leroy@c-s.fr

arch/powerpc/platforms/8xx/cpm1.c

@@ -51,7 +51,7 @@
 #define CPM_MAP_SIZE    (0x4000)
 
 cpm8xx_t __iomem *cpmp;  /* Pointer to comm processor space */
-immap_t __iomem *mpc8xx_immr;
+immap_t __iomem *mpc8xx_immr = (void __iomem *)VIRT_IMMR_BASE;
 static cpic8xx_t __iomem *cpic_reg;
 
 static struct irq_domain *cpm_pic_host;
@@ -201,12 +201,6 @@ void __init cpm_reset(void)
 {
 	sysconf8xx_t __iomem *siu_conf;
 
-	mpc8xx_immr = ioremap(get_immrbase(), 0x4000);
-	if (!mpc8xx_immr) {
-		printk(KERN_CRIT "Could not map IMMR\n");
-		return;
-	}
-
 	cpmp = &mpc8xx_immr->im_cpm;
 
 #ifndef CONFIG_PPC_EARLY_DEBUG_CPM