arm/imx: don't depend on ARCH_MXC twice

MXC_IRQ_PRIOR, MXC_PWM and ARCH_HAS_RNGA are all defined in an "if
ARCH_MXC" ... "endif" block, so they depend on ARCH_MXC anyhow.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

arch/arm/plat-mxc/Kconfig

@@ -48,7 +48,6 @@ endmenu
 
 config MXC_IRQ_PRIOR
 	bool "Use IRQ priority"
-	depends on ARCH_MXC
 	help
 	  Select this if you want to use prioritized IRQ handling.
 	  This feature prevents higher priority ISR to be interrupted
@@ -59,7 +58,6 @@ config MXC_IRQ_PRIOR
 
 config MXC_PWM
 	tristate "Enable PWM driver"
-	depends on ARCH_MXC
 	select HAVE_PWM
 	help
 	  Enable support for the i.MX PWM controller(s).
@@ -69,7 +67,6 @@ config MXC_ULPI
 
 config ARCH_HAS_RNGA
 	bool
-	depends on ARCH_MXC
 
 config ARCH_MXC_IOMUX_V3
 	bool