arc: get rid of DEVTMPFS dependency on INITRAMFS_SOURCE

Even though DEVTMPFS is required when our pre-built initramfs
is used it is not the case in general. It is perfectly possible
to use initramfs with device nodes already populated or there
could be other usages, see discussion below for more detials:
http://thread.gmane.org/gmane.comp.embedded.openwrt.devel/37819/focus=37821

This change removes mentioned dependency from arch/arc/Kconfig
updating instead those defconfigs that are usually used with this
kind of pre-build initramfs.

And while at it all touched defconfigs were regenerated via
savedefconfig and some options were removed:
 * USB is selected by other options implicitly
 * VGA_CONSOLE is disableb for ARC since
   031e29b587
 * EXT3_FS automatically selects EXT4_FS
 * MTDxxx and JFFS2_FS make no sense for AXS because
   AXS NAND controller is not upstreamed
 * NET_OSCI_LAN is not in upstream as well
 * ARCPGU_xxx options make no sense because ARC PGU is not yet
   in upstream and when it gets there all config options would
   be taken from devicetree

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

arch/arc/configs/nsimosci_defconfig

@@ -33,6 +33,7 @@ CONFIG_UNIX_DIAG=y
 CONFIG_NET_KEY=y
 CONFIG_INET=y
 # CONFIG_IPV6 is not set
+CONFIG_DEVTMPFS=y
 # CONFIG_STANDALONE is not set
 # CONFIG_PREVENT_FIRMWARE_BUILD is not set
 # CONFIG_FIRMWARE_IN_KERNEL is not set
@@ -58,7 +59,6 @@ CONFIG_SERIAL_OF_PLATFORM=y
 # CONFIG_HW_RANDOM is not set
 # CONFIG_HWMON is not set
 CONFIG_FB=y
-# CONFIG_VGA_CONSOLE is not set
 CONFIG_FRAMEBUFFER_CONSOLE=y
 CONFIG_LOGO=y
 # CONFIG_HID is not set