omap: Use a memory address for storing the debug port info instead of UART1 scratchpad

This removes the dependency to the UART1 being available for storing
the debug configuration in uncompress.h. This will simplify the
DEBUG_LL UART configuration for boards that may not have UART1, or
have an external UART as it requires only one mapping for DEBUG_LL.

The patch has a few limitations. Basically now we're assuming that
the kernel uncompress code won't overlap with OMAP_UART_INFO. We also
assume the printascii is called at least once before paging_init in
order for addruart to have a chance to read the UART setup from
OMAP_UART_INFO.

As suggested by Cyril Chemparathy <cyril@ti.com>,
Vikram Pandita <vikram.pandita@ti.com> and
Kevin Hilman <khilman@deeprootsystems.com>. Based on an earlier
patch posted for Davinci by Cyril Chemparathy <cyril@ti.com>.

Signed-off-by: Tony Lindgren <tony@atomide.com>