Revert "Kernel Driver: Update buffer mapping ops in IRQ"

This reverts commit d8f80e76722e721e56fd743be38afd088ad3df50.
Kernel Driver: Implement lseek() for mmap'd stuff

Also, a little change in data structure organization, RFU

Signed-off-by: Kumar Abhishek <abhishek@theembeddedkitchen.net>
Kernel Driver: read() does not ignore buf=NULL

lseek() to be used instead

Signed-off-by: Kumar Abhishek <abhishek@theembeddedkitchen.net> (reverted from commit e113e91793cd0af0206f6683f9a20f93b3bf57bf)