Some consoles, like the input console (usually /dev/cs0), don't feature
a puts or putc callback. Trying to echo out of them would thus crash:

	barebox@Embest MarS Board i.MX6Dual:/ echo -a /dev/cs0
	prefetch abort
	pc : [<00000004>]    lr : [<4fd05071>]
	WARNING: [<...>] (fops_write+0xd/0x10)
	WARNING: [<...>] (devfs_write+0x21/0x2a)
	WARNING: [<...>] (__write+0xcb/0xf0)
	WARNING: [<...>] (write+0x2d/0x68)
	WARNING: [<...>] (dputc+0x31/0x34)
	WARNING: [<...>] (do_echo+0xcb/0x144)

Fix this by only allowing open(.., O_WRONLY) or open(..., O_RDWR) when
puts is defined. Consoles defining putc are covered by this as well as
those have putc-calling __console_puts assigned as their puts when they
are registered. Now echo -a /dev/cs0 would yield:

	open: Operation not permitted

Signed-off-by: Ahmad Fatoum <ahmad@a3f.at>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>