arm64: dts: r8a7795: Increase the size of GIC-400 mapped registers

There are some requirements about the GIC-400 memory layout and its
mapping if using 64k aligned base addresses like on r8a7795.

See e.g.

http://xenbits.xen.org/gitweb/?p=xen.git;a=commit;h=21550029f709072aacf3b9



Map the whole memory range instead of only 0x2000. This will fix
the issue that some hypervisors, e.g. Xen, fail to handle the
interrupts correctly.

Signed-off-by: Pooya Keshavarzi <Pooya.Keshavarzi@de.bosch.com>
Signed-off-by: Dirk Behme <dirk.behme@de.bosch.com>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>