ARM: 8379/1: disable CONFIG_PTDUMP on !MMU

It's obviously pointless to dump page tables when the MMU is disabled,
and even trying to build this code results in numerous build errors
like these:

../arch/arm/mm/dump.c:56:11: error: 'L_PTE_USER' undeclared here (not in a function)
   .mask = L_PTE_USER,
           ^
../arch/arm/mm/dump.c:61:11: error: 'L_PTE_RDONLY' undeclared here (not in a function)
   .mask = L_PTE_RDONLY,
           ^
../arch/arm/mm/dump.c:66:11: error: 'L_PTE_XN' undeclared here (not in a function)
   .mask = L_PTE_XN,
           ^

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>