Simplify linker script to remove preprocessing, not check flash sizes

Memory layout is now split into two linker scripts for OTA vs
non-OTA (different starting offsets), remaining functionality in
common.ld.

As discussed in #64, progress towards #38

ld/ota.ld

@@ -0,0 +1,15 @@
+/* Memory layout for esp-open-rtos when using OTA second stage bootloader */
+
+MEMORY
+{
+  dport0_0_seg :                      	org = 0x3FF00000, len = 0x10
+  dram0_0_seg :                       	org = 0x3FFE8000, len = 0x14000
+  iram1_0_seg :                       	org = 0x40100000, len = 0x08000
+/* irom0 section, mapped from SPI flash
+  - Origin is offset by 0x2010 to create spacer for second stage bootloader image,
+    header.
+
+  - Length is max 8Mbit of mappable flash, minus start offset
+*/
+  irom0_0_seg :                       	org = 0x40202010, len = (1M - 0x2010)
+}