x86/kconfig: Remove X86_DIRECT_GBPAGES dependency on !DEBUG_PAGEALLOC

These days CONFIG_DEBUG_PAGEALLOC just compiles in the code that has to be
enabled on boot time, or with an extra config option, and only then are the
large page based direct mappings disabled.

Therefore remove the config dependency, allowing 1GB direct mappings with
debug_pagealloc compiled in but not enabled.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190807130258.22185-1-vbabka@suse.cz