microblaze: Calculate kernel pad automatically

The kernel needs to setup the first two tlbs with pad
which is used for early page allocation which is used
by mapin_ram() to allocate tables for lowmem memory
before memory initialisation is done.
Calculate pad directly from lowmem size.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>

arch/microblaze/Kconfig

@@ -245,10 +245,6 @@ config MICROBLAZE_64K_PAGES
 
 endchoice
 
-config KERNEL_PAD
-	hex "Kernel PAD for unpacking" if ADVANCED_OPTIONS
-	default "0x80000" if MMU
-
 endmenu
 
 source "mm/Kconfig"

arch/microblaze/kernel/head.S

@@ -176,7 +176,7 @@ _invalidate:
 	/* start to do TLB calculation */
 	addik	r12, r0, _end
 	rsub	r12, r3, r12
-	addik	r12, r12, CONFIG_KERNEL_PAD /* that's the pad */
+	addik	r12, r12, CONFIG_LOWMEM_SIZE >> PTE_SHIFT /* that's the pad */
 
 	or r9, r0, r0 /* TLB0 = 0 */
 	or r10, r0, r0 /* TLB1 = 0 */