CBMEM CONSOLE: Add config option for CBMEM stored console log.

CBMEM CONSOLE: Add config option for CBMEM stored console log.

Some experiments have demonstrated that total amount of text
generated by coreboot console when BIOS_SPEW level is enabled
exceeds 40KB.

Console output generated before DRAM is initialized can exceed
2KB. This patch introduces the new configuration option and
assigns adequate default values to cache based and DRAM based
console buffers.

BUG=chrome-os-partner:4200
TEST=manual

 . run the following commands in the root directory

   cp config.stumpy .config
   make menuconfig

 . enable the new option (Console->Send console output to a CBMEM buffer)
 . save the configuration

Observe the following settings added to the config:
+CONFIG_CONSOLE_CBMEM=y
+CONFIG_CONSOLE_CBMEM_BUFFER_SIZE=0xae00
+CONFIG_CONSOLE_CAR_BUFFER_SIZE=0xc00

Change-Id: I209603f516244ae136631e6281ba21ebc6fb1710
Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-on: https://gerrit-int.chromium.org/5855
Tested-by: Vadim Bendebury <vbendeb@google.com>
Reviewed-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/718
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>