mtd: jz4740_nand: fix build on jz4740 after removing gpio.h

mtd: jz4740_nand: fix build on jz4740 after removing gpio.h

Fallout from commit 832f5dacfa0b ("MIPS: Remove all the uses of custom gpio.h")

We see errors like this:

drivers/mtd/nand/jz4740_nand.c: In function 'jz_nand_detect_bank':
drivers/mtd/nand/jz4740_nand.c:340:9: error: 'JZ_GPIO_MEM_CS0' undeclared (first use in this function)
drivers/mtd/nand/jz4740_nand.c:340:9: note: each undeclared identifier is reported only once for each function it appears in
drivers/mtd/nand/jz4740_nand.c:359:2: error: implicit declaration of function 'jz_gpio_set_function' [-Werror=implicit-function-declaration]
drivers/mtd/nand/jz4740_nand.c:359:29: error: 'JZ_GPIO_FUNC_MEM_CS0' undeclared (first use in this function)
drivers/mtd/nand/jz4740_nand.c:399:29: error: 'JZ_GPIO_FUNC_NONE' undeclared (first use in this function)
drivers/mtd/nand/jz4740_nand.c: In function 'jz_nand_probe':
drivers/mtd/nand/jz4740_nand.c:528:13: error: 'JZ_GPIO_MEM_CS0' undeclared (first use in this function)
drivers/mtd/nand/jz4740_nand.c: In function 'jz_nand_remove':
drivers/mtd/nand/jz4740_nand.c:555:14: error: 'JZ_GPIO_MEM_CS0' undeclared (first use in this function)

Patched similarly to:

https://patchwork.linux-mips.org/patch/11089/

Fixes: 832f5dacfa0b ("MIPS: Remove all the uses of custom gpio.h")
Signed-off-by: Brian Norris <computersforpeace@gmail.com>