LoongArch: Drop these obsolete selects in Kconfig

Commit fa96b57c ("LoongArch: Add build infrastructure") adds the new
file arch/loongarch/Kconfig.

As the work on LoongArch was probably quite some time under development,
various config symbols have changed and disappeared from the time of
initial writing of the Kconfig file and its inclusion in the repository.

The following four commits:

  commit c126a53c ("arch: remove GENERIC_FIND_FIRST_BIT entirely")
  commit 140c8180 ("arch: remove HAVE_COPY_THREAD_TLS")
  commit aca52c39 ("mm: remove CONFIG_HAVE_MEMBLOCK")
  commit 3f08a302 ("mm: remove CONFIG_HAVE_MEMBLOCK_NODE_MAP option")

remove the mentioned config symbol, and enable the intended setup by
default without configuration.

Drop these obsolete selects in loongarch's Kconfig.

Reviewed-by: WANG Xuerui <git@xen0n.name>
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>