csky: Kconfig: Remove unused selects

 - GENERIC_ALLOCATOR is duplicated
 - Remove USB_ARCH_HAS_OHCI & USB_ARCH_HAS_EHCI, because they
   have been removed from linux.

Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Cc: Arnd Bergmann <arnd@arndb.de>