Add userland driver to spi framework.

Previously spi would configure the controller to use the lowest speed of
all connected devices since the kernel started and to fail attempted mode
changes. This

Add userland driver to spi framework.

Previously spi would configure the controller to use the lowest speed of
all connected devices since the kernel started and to fail attempted mode
changes. This is now improved to keep individual modes and speeds for each
slave and to reconfigure the controller as necessary for each transfer.

Added man page for spi(9).

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