arm64: dts: juno: fix size of GICv2m MSI frames

Currently the size of GICv2m MSI frames are listed as 4kB while the
Juno TRM specifies 64kB for each of these MSI frames.

Though the devices connected themselves might just use the first 4kB,
to be consistent with the general practice of 64kB boundary alignment
to all the devices, let's keep the size as 64kB. This might also help
in avoiding any surprise when passing the device to a VM.

This patch increases the size of each GICv2m MSI frames from 4kB to 64kB
as per the specification.

Cc: Liviu Dudau <liviu.dudau@arm.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>