mips: alchemy: remove historic comment on gpio build constraints

In ./arch/mips/alchemy/common/gpiolib.c, the comment points out certain
build constraints on CONFIG_GPIOLIB and CONFIG_ALCHEMY_GPIO_INDIRECT.

The commit 832f5dacfa0b ("MIPS: Remove all the uses of custom gpio.h")
makes all mips machines use the common gpio.h and removes the config
ALCHEMY_GPIO_INDIRECT. So, this makes the comment in alchemy's gpiolib.c
historic and obsolete, and can be removed after the commit above.

The issue on the reference to a non-existing Kconfig symbol was identified
with ./scripts/checkkconfigsymbols.py. This script has been quite useful
to identify a number of bugs with Kconfig symbols and deserves to be
executed and checked regularly.

So, remove the historic comment to reduce the reports made the script and
simplify to use this script, as new issues are easier to spot when the
list of reports is shorter.

Signed-off-by: Lukas Bulwahn <[e-mail]>
Signed-off-by: Thomas Bogendoerfer <[e-mail]>

arch/mips/alchemy/common/gpiolib.c

···
  *  675 Mass Ave, Cambridge, MA 02139, USA.
  *
  *  Notes :
- *	This file must ONLY be built when CONFIG_GPIOLIB=y and
- *	 CONFIG_ALCHEMY_GPIO_INDIRECT=n, otherwise compilation will fail!
  *	au1000 SoC have only one GPIO block : GPIO1
  *	Au1100, Au15x0, Au12x0 have a second one : GPIO2
  *	Au1300 is totally different: 1 block with up to 128 GPIOs