drivers/char: Add export.h for EXPORT_SYMBOL/THIS_MODULE as required

They will need it called out explicitly in the near future due
to a module.h usage cleanup that removes its implicit presence
everywhere.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --cc drivers/char/mem.c
Simple merge

diff --cc drivers/char/ttyprintk.c
Simple merge