kernel: fix missing TRANSPARENT_HUGEPAGE symbols

kernel: fix missing TRANSPARENT_HUGEPAGE symbols

Enabling KERNEL_TRANSPARENT_HUGEPAGE exposes 2 missing symbols:
* CONFIG_READ_ONLY_THP_FOR_FS
* TRANSPARENT_HUGEPAGE_ALWAYS
* TRANSPARENT_HUGEPAGE_MADVISE

The first one was added in 5.4, and is marked experimental there so just
disable it in the generic config.

For the latter two, we should not force the user to use either of them,
so add them as build-configurable kernel options.

Fixes: d1a8217d87bf ("kernel: clean-up build-configurable kernel config symbols")
Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>