Replace CONFIG_SYS_GBL_DATA_SIZE by auto-generated value

CONFIG_SYS_GBL_DATA_SIZE has always been just a bad workarond for not
being able to use "sizeof(struct global_data)" in assembler files.
Recent experience has shown that manual synchronization is not
reliable enough.  This patch renames CONFIG_SYS_GBL_DATA_SIZE into
GENERATED_GBL_DATA_SIZE which gets automatically generated by the
asm-offsets tool.  In the result, all definitions of this value can be
deleted from the board config files.  We have to make sure that all
files that reference such data include the new <asm-offsets.h> file.

No other changes have been done yet, but it is obvious that similar
changes / simplifications can be done for other, related macro
definitions as well.

Signed-off-by: Wolfgang Denk <wd@denx.de>
Acked-by: Kumar Gala <galak@kernel.crashing.org>