gpio/aspeed-sgpio: enable access to all 80 input & output sgpios

Currently, the aspeed-sgpio driver exposes up to 80 GPIO lines,
corresponding to the 80 status bits available in hardware. Each of these
lines can be configured as either an input or an output.

However, each of these GPIOs is actually an input *and* an output; we
actually have 80 inputs plus 80 outputs.

This change expands the maximum number of GPIOs to 160; the lower half
of this range are the input-only GPIOs, the upper half are the outputs.
We fix the GPIO directions to correspond to this mapping.

This also fixes a bug when setting GPIOs - we were reading from the
input register, making it impossible to set more than one output GPIO.

Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Fixes: 7db47faa ("gpio: aspeed: Add SGPIO driver")
Reviewed-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Andrew Jeffery <andrew@aj.id.au>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>