sdmmc1 for stm32F7 74-75

Add some CAN mode IOCTL calls.  These will be useful for device autotest when the application boots.  They are redundant with the CONFIG_CAN_LOOPBACK option, which can now just be interpreted as a default setting.

syslog_dev_flush() needs to check if the inode is a mountpoint before calling the flush() method.  Noted by David Sidrane.

can: Add support for poll

SYSLOG: Change configuration selections to assure that one and only one SYSLOG device can be selected.  Also add a check to assure that it is appropriate to use up_putc as the low-level syslog device.  Adds CONFIG_SYSLOG_CONSOLE and CONFIG_SYSLOG_SERIAL_CONSOLE.

SYSLOG: Now a two phase initialization. Some SYSLOG channels cannot be initialized until later in the bringup