More generic working kernel (also works on Alpha 5).

After A LOT of testing i made this kernel config. I think it's best of both worlds and also fits the XBian spirit better.

All changes with comments:

1. GZIP compressed kernel
_I could not get a XZ compressed kernel to work. I tried about everything. For portability, lets just stick with gzip._
2. gzip / bzip2 compressed ramfs
_I re-enabled the possibility to use gzip and bzip2 compressed initramfs devices. The goal of XBian is to be modular and bleeding edge. Removing the gzip and bzip2 compressed initramfs devices, will also reduce the modularity of the XBian kernel. Would users want to use existing initramfs solutions, they can't easily do without it (like the Alpha 5 initramfs)._
3. I've inserted the EXT[2/3/4] and BTRFS filesystem drivers in the kernel instead of having them a module. This gives the user more freedom. They can choose not the use a initramfs and use other filesystem types than BTRFS. More importantly, if the initramfs should fail, they can still boot and create a new one.

Point 2 and 3 enables this kernel to be used in Alpha 5. This way, the dependency to the initramfs can be removed and the kernel can just check if the initramfs-tools are available and use them. If not, the kernel will just work. So, again more modularity and more user friendly by giving users more choices.

And in size, what are we talking about. The current kernel is 3mb, i don't think the 1.5mb is worth all the trouble.