drivers: wifi: nxp: add heap for NXP Wi-Fi

Use HEAP_MEM_POOL_ADD_SIZE_ to add heap for NXP Wi-Fi. For supplicant
case, define less heap, as CONFIG_HEAP_MEM_POOL_ADD_SIZE_HOSTAP and
CONFIG_HEAP_MEM_POOL_ADD_SIZE_SOCKETPAIR are also enabled.

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