Merge tag 'arc-for-2018.05' of git://git.denx.de/u-boot-arc

More ARC changes and fixes for v2018.05

 * Update of ARC tools to the most recent arc-2017.09
 * Fix for compile-time warning for AXS10x
 * Add support of platform-specific commands for HSDK
 * Add support for on-board SPI flash on HSDK
   Note though that for write support another series [1]
   is required. I hope that Jagan will be able to review and
   act on SPI flash improvement series before we get beyond RC1.

   Also note that to get clean build for HSDK we need to disable
   stack-usage check [2] as our current GCC erroneously tries to calculate
   stack-usage on a naked function which leads to warning.

[1] https://patchwork.ozlabs.org/project/uboot/list/?series=35796
[2] https://patchwork.ozlabs.org/patch/894139/