hostap: update the default heap size for hostap

As kernel heap is used for hostap, which replaced libc heap, then no
need to consider the MBEDTLS_ENABLE_HEAP case. For enterprise case,
mbedtls will use MBEDTLS_HEAP or libc heap to allocate memory, instead
of the kernel heap.
Modify the heap size for enterprise case to have necessary memory.

Signed-off-by: Maochen Wang <maochen.wang@nxp.com>