ARC: [axs101] Recovering some more performance

Basic system parameters
--------------------------------------------------------------------------------------
        Host                 OS Description Mhz  tlb  cache  mem   scal
                                                pages line   par   load
                                                      bytes
----------------- ------------- --------------------------------------- ---- ----- ----- ------ ----
axs101-sd-2-new-f Linux 3.13.0+ axs101-sd-2-new-fw-old-img-rerun 739     8    32 1.1100    1
axs101-sd-3-arc-3 Linux 3.13.9+ axs101-sd-3-arc-3.13-tip-regression 735     8    32 1.1000    1
axs101-sd-7-tweak Linux 3.13.9- axs101-sd-7-tweak-axi-mem-map-BEST 738     8    32 1.0000    1
axs101-sd-9-diffe Linux 3.13.11 axs101-sd-9-different-tweak 740     8    32 1.0000    1

Processor, Processes - times in microseconds - smaller is better
------------------------------------------------------------------------------
Host                 OS  Mhz null null      open slct sig  sig  fork exec sh
                             call  I/O stat clos TCP  inst hndl proc proc proc
--------- ------------- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----
axs101-sd Linux 3.13.0+  739 0.50 0.88 5.38 14.6 34.1 0.92 5.18 2135 6555 12.K
axs101-sd Linux 3.13.9+  735 0.50 0.90 5.89 19.2 81.4 0.94 4.08 2560 8559 15.K
axs101-sd Linux 3.13.9-  738 0.50 0.90 5.05 16.0 71.2 0.94 3.75 2038 6312 11.K (prev fix)
axs101-sd Linux 3.13.11  740 0.50 0.88 4.45 17.8 34.4 0.94 3.25 2052 6493 12.K (this one)
                                                 ^^^^

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
ARC: support external initrd [3.15 backport]

Currently ARC only supports embedded initrd. This patch enables
external ones too.

[vgupta: Changed from "rt_start"=start/"rd_size"=sz to unified "initrd"=start,sz]
Signed-off-by: Noam Camus <noamc@ezchip.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>