MIPS: BCM63XX: Add missing include for bcm63xx_gpio.h

bcm63xx_gpio.h uses macros defined in bcm63xx_cpu.h without including it,
leading to the following build failure:

  CC [M]  drivers/mmc/core/cd-gpio.o
In file included from arch/mips/include/asm/mach-bcm63xx/gpio.h:4:0,
                 from arch/mips/include/asm/gpio.h:4,
                 from include/linux/gpio.h:30,
                 from drivers/mmc/core/cd-gpio.c:12:

arch/mips/include/asm/mach-bcm63xx/bcm63xx_gpio.h: In function 'bcm63xx_gpio_count':
arch/mips/include/asm/mach-bcm63xx/bcm63xx_gpio.h:10:2: error: implicit declaration of function 'bcm63xx_get_cpu_id'
arch/mips/include/asm/mach-bcm63xx/bcm63xx_gpio.h:11:7: error: 'BCM6358_CPU_ID' undeclared (first use in this function)
arch/mips/include/asm/mach-bcm63xx/bcm63xx_gpio.h:11:7: note: each undeclared identifier is reported only once for each function it appears in
arch/mips/include/asm/mach-bcm63xx/bcm63xx_gpio.h:13:7: error: 'BCM6338_CPU_ID' undeclared (first use in this function)
arch/mips/include/asm/mach-bcm63xx/bcm63xx_gpio.h:15:7: error: 'BCM6345_CPU_ID' undeclared (first use in this function)
arch/mips/include/asm/mach-bcm63xx/bcm63xx_gpio.h:17:7: error: 'BCM6368_CPU_ID' undeclared (first use in this function)
arch/mips/include/asm/mach-bcm63xx/bcm63xx_gpio.h:19:7: error: 'BCM6348_CPU_ID' undeclared (first use in this function)

make[7]: *** [drivers/mmc/core/cd-gpio.o] Error 1

Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
Cc: stable@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: Maxime Bizon <mbizon@freebox.fr>
Cc: Florian Fainelli <florian@openwrt.org>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>