printk: collect printk stuff into <linux/printk.h> with loglevel support

When we import code from Linux, with regular re-sync planned, we want
to use printk() and pr_*().  U-Boot does not support them in a clean
way.  So, people end up with local macros, or compat headers here and
there, then we occasionally see build errors of definition conflicts.

We have include/linux/compat.h, but putting all sorts of unrelated
things into a single header is just a temporal workaround.  Hence this
patch, to find the best home for all printk variants.  If you want to
use printk() and friends, please include <linux/printk.h>.  This header
is self-contained, and pulls in only a few headers.

When I was testing this clean-up, I noticed the image size exceeded
its platform limit on some boards.  This is because all pr_*() that
were previously defined as no-op in include/linux/mtd/mtd.h (unless
CONFIG_MTD_DEBUG is set), are now enabled.

To make such boards happy, this commit also implements CONFIG_LOGLEVEL.
The concept is similar to the kernel parameter "loglevel".  (Actually,
the Kconfig help message was taken from kernel-paremeter.txt of Linux)
Messages with a loglevel smaller than console loglevel will be printed.

The difference is the loglevel is build-time determined.  To save the
image size, lower priority pr_*() are compiled out.  I set the default
of CONFIG_LOGLEVEL to 6, i.e. pr_notice and higher priority messages
are compiled in.

I adjusted CONFIG_LOGLEVEL to avoid build error for some boards.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
[trini: Add in SPL_LOGLEVEL that is the same as LOGLEVEL]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/common/Kconfig b/common/Kconfig
index 540cc99..f53ee9d 100644
--- a/common/Kconfig
+++ b/common/Kconfig
@@ -241,6 +241,27 @@
 	help
 	  This options adds the board specific name to u-boot version.
 
+config LOGLEVEL
+	int "loglevel"
+	default 6
+	range 0 8
+	help
+	  All Messages with a loglevel smaller than the console loglevel will
+	  be compiled in. The loglevels are defined as follows:
+
+	  0 (KERN_EMERG)          system is unusable
+	  1 (KERN_ALERT)          action must be taken immediately
+	  2 (KERN_CRIT)           critical conditions
+	  3 (KERN_ERR)            error conditions
+	  4 (KERN_WARNING)        warning conditions
+	  5 (KERN_NOTICE)         normal but significant condition
+	  6 (KERN_INFO)           informational
+	  7 (KERN_DEBUG)          debug-level messages
+
+config SPL_LOGLEVEL
+	int
+	default LOGLEVEL
+
 config SILENT_CONSOLE
 	bool "Support a silent console"
 	help