MPC85xx: TQM8548: use cache for AG and BE variants

This patch makes accesses to the system memory cachable by removing the
caching-inhibited and guarded flags from the relevant TLB entries for
the TQM8548_BE and TQM8548_AG modules. FYI, the Freescale MPC85* boards
are configured similarly.

This results in a big averall performace improvement. TFTP downloads,
NAND Flash accesses, kernel boots, etc. are much faster.

Signed-off-by: Wolfgang Grandegger <wg@grandegger.com>