tee: refactor TEE_SHM_* flags

Removes the redundant TEE_SHM_DMA_BUF, TEE_SHM_EXT_DMA_BUF,
TEE_SHM_MAPPED and TEE_SHM_KERNEL_MAPPED flags.

TEE_SHM_REGISTER is renamed to TEE_SHM_DYNAMIC in order to better
match its usage.

Assigns new values to the remaining flags to void gaps.

Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>