Fix OS X crossbuilds for arm

- Fixed missing variable interpolation because of single quotes
 - Replaced /bin/sh in gen_uEnv.txt.sh with /usr/bin/env bash as the default
   echo doesn't support '-n'
 - Fixed some whitespace errors
 - A succesful build requires for now to skip the gold linker on OSX.

Change-Id: Id09bf52f45252026e3a58b74e8448ea24a0dab12

releasetools/arm_sdimage.sh

@@ -79,7 +79,7 @@ HOME_START=$(($USR_START + $USR_SIZE))
 case $(uname -s) in
 Darwin)
 	MKFS_VFAT_CMD=newfs_msdos
-	MKFS_VFAT_OPTS='-h 64 -u 32 -S 512 -s ${FAT_SIZE} -o 0'
+	MKFS_VFAT_OPTS="-h 64 -u 32 -S 512 -s ${FAT_SIZE} -o 0"
 ;;
 FreeBSD)
 	MKFS_VFAT_CMD=newfs_msdos

releasetools/gen_uEnv.txt.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/usr/bin/env bash
 
 #generate a u-boot u-env.
 list="0x80200000 kernel.bin