boot: only show vendor-specific bootloaders for applicable arm variant

Atmel at91sam9 and NXP lpc32xx are both all arm926t, so only show
then if that arm variant is selected.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

boot/at91bootstrap/Config.in

@@ -1,5 +1,5 @@
 config BR2_TARGET_AT91BOOTSTRAP
-	depends on BR2_arm
+	depends on BR2_arm926t
 	bool "AT91 Bootstrap"
 	help
 	  AT91Bootstrap is a first level bootloader for the Atmel AT91

boot/at91dataflashboot/Config.in

@@ -1,3 +1,3 @@
 config BR2_TARGET_AT91DATAFLASHBOOT
-       depends on BR2_arm
+       depends on BR2_arm926t
        bool "AT91 DataFlashBoot"

boot/lpc32xxcdl/Config.in

@@ -1,5 +1,5 @@
 config BR2_TARGET_LPC32XXCDL
-	depends on BR2_arm
+	depends on BR2_arm926t
 	bool "LPC32XX CDL (kickstart and S1L)"
 
 if BR2_TARGET_LPC32XXCDL