arm: spear: Fix the main comment in start.S

This comment describes the board state at the moment where we enter
the SPL. The description is entirely wrong; re-write it to fit the
reality.
Signed-off-by: NMiquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: NStefan Roese <sr@denx.de>

arch/arm/cpu/arm926ejs/spear/start.S

@@ -21,10 +21,9 @@
  *
  * Startup Code (reset vector)
  *
- * Below are the critical initializations already taken place in BootROM.
- * So, these are not taken care in Xloader
- * 1. Relocation to RAM
- * 2. Initializing stacks
+ * The BootROM already initialized its own stack in the [0-0xb00] reserved
+ * range of the SRAM. The SPL (in _main) will update the stack pointer to
+ * its own SRAM area (right before the gd section).
  *
  *************************************************************************
  */