x86: increase the kernel text limit to 512 MB

people sometimes do crazy stuff like building really large static
arrays into their kernels or building allyesconfig kernels. Give
more space to the kernel and push modules up a bit: kernel has
512 MB and modules have 1.5 GB.

Should be enough for a few years ;-)

Signed-off-by: Ingo Molnar <mingo@elte.hu>