ARM: shmobile: r8a7740: add MERAM work-around

r8a7740 chip has lasting errata on MERAM buffer, and this patch adds
its work-around on setup-r8a7740.c
It solved CEU/VIO6C/2D-DMAC/VCP1/VPU5F/JPU/DISP memroy access error.

But MERAM driver can't control this issue,
since this work-around requires access to non-MERAM register address.
So, This it will be called as board specific code at this point.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Tested-by: Simon Horman <horms@verge.net.au>
Acked-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>