commit 961c0eac ('x86: fix lifting kernel CPU requirements and always
enable PAE') broke some older geode boards such as Soekris net4826.
Hence disable PAE on x86/legacy again in order to still support those
very old non-PAE capable CPUs.

Fixes FS#773 - PAE broke Soekris net4826

Signed-off-by: Daniel Golle <daniel@makrotopia.org>