И всё же мне кажется, что в собранном вами ядре отсутствует поддержка следующих опций:
Intel 440LX/BX/GX, I8xx and E7x05 chipset support (AGP_INTEL)
CONFIG_AGP_INTEL:
This option gives you AGP support for the GLX component of X
on Intel 440LX/BX/GX, 815, 820, 830, 840, 845, 850, 860, 875,
E7205 and E7505 chipsets and full support for the 810, 815, 830M,
845G, 852GM, 855GM, 865G and I915 integrated graphics chipsets.
Intel 8xx/9xx/G3x/G4x/HD Graphics (DRM_I915)
CONFIG_DRM_I915:
Choose this option if you have a system that has "Intel Graphics
Media Accelerator" or "HD Graphics" integrated graphics,
including 830M, 845G, 852GM, 855GM, 865G, 915G, 945G, 965G,
G35, G41, G43, G45 chipsets and Celeron, Pentium, Core i3,
Core i5, Core i7 as well as Atom CPUs with integrated graphics.
If M is selected, the module will be called i915. AGP support
is required for this driver to work. This driver is used by
the Intel driver in X.org 6.8 and XFree86 4.4 and above. It
replaces the older i830 module that supported a subset of the
hardware in older X.org releases.
Note that the older i810/i815 chipsets require the use of the
i810 driver instead, and the Atom z5xx series has an entirely
different implementation.
Так как в выводе команды lspci -k у вас отсутствует строка
# lspci -k | grep VGA -A 2 [gentoo-laptop][10:49]
00:02.0 VGA compatible controller: Intel Corporation Mobile 945GM/GMS, 943/940GML Express Integrated Graphics Controller (rev 03)
Subsystem: Toshiba America Info Systems Device ff01
Kernel driver in use: i915
Да и в /var/log/Xorg.0.log есть ошибки связанные с отсутствием устройства.
Был, был и весь вышел...
