From: Martin Schwidefsky <schwidefsky@de.ibm.com>

SCLP console/tty fixes:

- Fix incorrect state change of SCLP_RUNNING flag in interrupt handler

- Suppress emission of empty buffers to prevent stack overflow

- Fix off by one error in sclp_write (used to return # of chars written + 1)

- Prevent sclp_tty_write_string from waiting in interrupt (during flush)

- Fix deadlock after TIOCSCLPSNL ioctl

- Fix sclp_tty_chars_in_buffer calculation