erofs: move erofs_xattr_handlers and xattr_handler_map to .rodata

erofs: move erofs_xattr_handlers and xattr_handler_map to .rodata

This makes it harder for accidental or malicious changes to
erofs_xattr_handlers or xattr_handler_map at runtime.

Cc: Gao Xiang <xiang@kernel.org>
Cc: Chao Yu <chao@kernel.org>
Cc: Yue Hu <huyue2@coolpad.com>
Cc: Jeffle Xu <jefflexu@linux.alibaba.com>
Cc: linux-erofs@lists.ozlabs.org
Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
Link: https://lore.kernel.org/r/20230930050033.41174-9-wedsonaf@gmail.com
Acked-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>