seoul: enable -Wall and fix warnings

Issue #1262
seoul: update pae branch

Fixes #1262
VFS: acquire tar dataspace only once

Fixes #1271
hw: don't preserve mmio of core devices

Fixes #1269
hw/rpi: USB SOF interrupt filtering
dde_linux: USB SOF IRQ filter for Raspberry Pi
libports: rpi support in lwip.run
ports: rpi support in netperf run scripts
init: use file name as label for redirected ROMs
dynamic_rom: remove superfluous sigh dissolve

The 'Signal_rpc_member' takes care about dissolving its signal context
from the receiver. So we don't need to manually perform this operation
in the session destructor.
nitpicker: consider xray config in find_view

If a domain is configured as xray="no", we want to let the views of the
domain respond to input events like in flat mode, even if xray mode is
active. Normally, the input mask of views with an alpha channel is
disregarded in X-ray mode. However, for non-ray views, the input mask
should always be considered.
nitpicker: fix input-mask offset calculation

The buffer offset was wrongly accounted for. The miscalculation went
unnoticed until now because the buffer offset was apparently never used
in combination with alpha-channels.
nitpicker: disable reports by default

Prior this change, a config update would not disable reports if the
report node disappeared during the update.
nitpicker: report xray mode
nitpicker: motion events for non-xray clients

When X-ray mode is active, nitpicker filters motion events that are not
referring to the currently focused domain. However, domains configured
as xray="no" (such as a panel) need to obtain motion events regardless
of the xray mode. This patch relaxes the motion-event filtering to
accommodate such clients.
base: add 'String::operator!='
os: define ALPHA8 pixel format
os: improve alpha-channel support for Pixel_rgba

This patch add an optional alpha argument to the constructor, which may
be passed to a pixel type representing an alpha channel. Furthermore,
a new overload of the mix function has been added to accommodate use
cases where one texture is applied to both a pixel surface and an alpha
channel.
gems: move reusable code to include/gems

This patch makes various utilities that were originally developed for
the backdrop application publicly available.
os: add texture_rgb888.h and texture_rgb565.h

The headers 'texture_rgb565.h' and 'texture_rgb888' contain
template specializations needed for using the 'Texture::rgba' function
for the respective pixel formats. The specializations were formerly
contained in application-local code.