exynos4, exynos5: add DTS overlay comments

This explains why the DTS overlays intentionally throw away part of
the kernel memory window.

src/plat/exynos4/overlay-exynos4.dts

@@ -16,6 +16,11 @@
 		device_type = "memory";
 	};
 
+	/* HACK: 0xe0000000..0xff000000 is the largest contiguous region
+	 * in the kernel window; we clamp to that and discard memory
+	 * after the ASID PD hole (0xff200000..0xfff00000). This is a
+	 * workaround for userspace tools (hardware_gen, elfloader, etc)
+	 * which are not yet aware of the memory hole. */
 	memory@40000000 {
 		device_type = "memory";
 		reg = < 0x40000000 0x1f000000 >;

src/plat/exynos5/overlay-exynos5250.dts

@@ -16,6 +16,11 @@
 		stdout-path = "serial2:115200n8";
 	};
 
+	/* HACK: 0xe0000000..0xff000000 is the largest contiguous region
+	 * in the kernel window; we clamp to that and discard memory
+	 * after the ASID PD hole (0xff200000..0xfff00000). This is a
+	 * workaround for userspace tools (hardware_gen, elfloader, etc)
+	 * which are not yet aware of the memory hole. */
 	memory@40000000 {
 		reg = <0x60000000 0x1f000000>;
 	};

src/plat/exynos5/overlay-exynos5410.dts

@@ -38,6 +38,11 @@
 		reg = <0x12d40000 0x100>;
 	};
 
+	/* HACK: 0xe0000000..0xff000000 is the largest contiguous region
+	 * in the kernel window; we clamp to that and discard memory
+	 * after the ASID PD hole (0xff200000..0xfff00000). This is a
+	 * workaround for userspace tools (hardware_gen, elfloader, etc)
+	 * which are not yet aware of the memory hole. */
 	memory@40000000 {
 		reg = <0x60000000 0x1f000000>;
 	};

src/plat/exynos5/overlay-exynos5422.dts

@@ -29,6 +29,11 @@
 		clock-frequency = <0x16e3600>;
 	};
 
+	/* HACK: 0xe0000000..0xff000000 is the largest contiguous region
+	 * in the kernel window; we clamp to that and discard memory
+	 * after the ASID PD hole (0xff200000..0xfff00000). This is a
+	 * workaround for userspace tools (hardware_gen, elfloader, etc)
+	 * which are not yet aware of the memory hole. */
 	memory@40000000 {
 		reg = <0x60000000 0x1f000000>;
 	};