When a poll requesting POLLOUT happens, the poll should return
immediately if a write will not block.  This change adds that, as
opposed to the old behaviour of blocking until a timer from the
Ethernet driver eventually triggers the poll to complete.

This is only implemented for buffered TCP.  Unbuffered TCP should
behave as before.

If stdout is a socket (e.g. telnet), then the debug message will cause
more TCP data to be sent, which generates another message, and so on

Fix romdisk_register prototype.  Most ROMFS images actually lie in RAM.  If moved to FLASH with const storage class, then changes are required to avoid warnings

Add LSM9DS1 accelerometer, gyroscope and magnetometer

add NXP pn532 NFC-chip support

Signed-off-by: Janne Rosberg <janne.rosberg@offcode.fi>