Work on contexts

apps/examples/crypto/crypto_main.c:
  Prepare key listing

nuttx/arch/arm/src/common/up_initialize.c:
  Include all prototypes

nuttx/crypto/cryptocore.c:
  module allocation done here, avoids an extern ref to modules_head

nuttx/crypto/cryptocore.h:
  improve context structure

nuttx/crypto/cryptodev.c:
  implemented context close
  implemented context info

nuttx/crypto/cryptomod.c:
  refactor to avoid references to modules_head
  avoid useless module name manipulations (and save 16 bytes of stack)

nuttx/include/nuttx/crypto/cryptomod.h:
  add a prototype for up_initialize