[POWERPC] Make the hvc_console output buffer size settable

So the iSeries console will be faster since it can send up to 200 bytes at
a time to the Hypervisor.  This only affects the tty part of the console,
the console writes are still in 16 byte lots.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>

diff --cc drivers/char/hvc_console.c
Simple merge

diff --cc drivers/char/hvc_console.h
Simple merge

diff --cc drivers/char/hvc_iseries.c
Simple merge

diff --cc drivers/char/hvc_rtas.c
Simple merge

diff --cc drivers/char/hvc_vio.c
Simple merge