microblaze: Remove architecture tlb.h and use generic one

There is no reason to have this empty file if it is just link to
asm-generic/tlb.h.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Stefan Asserhall <stefan.asserhall@xilinx.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>