sam3: Merge sam4e8e support into sam3 code

Most of the peripherals on the sam4e8e are similar to the ones on the
sam3x8e mcu.  Merge the code together and use just one code directory.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/sam3/Kconfig

@@ -1,12 +1,13 @@
-# Kconfig settings for SAM3 processors
+# Kconfig settings for SAM3/SAM4 processors
 
-if MACH_SAM3X8E
+if MACH_SAM3
 
-config SAM_SELECT
+config SAM3_SELECT
     bool
     default y
     select HAVE_GPIO
     select HAVE_GPIO_ADC
+    select HAVE_GPIO_I2C if MACH_SAM4E8E
     select HAVE_GPIO_SPI
     select HAVE_GPIO_BITBANGING
 
@@ -14,9 +15,23 @@ config BOARD_DIRECTORY
     string
     default "sam3"
 
+choice
+    prompt "Processor model"
+    config MACH_SAM3X8E
+        bool "SAM3x8e (Arduino Due)"
+    config MACH_SAM4E8E
+        bool "SAM4e8e (Duet Wifi/Eth)"
+endchoice
+
+config MCU
+    string
+    default "sam3x8e" if MACH_SAM3X8E
+    default "sam4e8e" if MACH_SAM4E8E
+
 config CLOCK_FREQ
     int
-    default 42000000 # 84000000/2
+    default 42000000 if MACH_SAM3X8E # 84000000/2
+    default 60000000 if MACH_SAM4E8E # 120000000/2
 
 config SERIAL
     bool