ARM: 9409/1: mmu: Do not use magic number for TTBCR settings

The code in early_paging_init is directly masking off bits
8, 9, 10 and 11 to temporarily disable caching of the translation
tables. There is some exlanations in the comment, but use some
defines instead of magic numbers so ut becomes more evident
what is going on.

Change the type of the register to u32 since these are indeed
unsigned 32bit registers, and use a temporary variable instead
of baking too much into the inline assembly call to increase
readability.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>