efibc: Report more information in the error messages

Report the name of the EFI variable if the value size is too large,
or if efibc_set_variable() fails to allocate the 'struct efivar_entry'
object.

If efibc_set_variable() fails because the 'size' value is too
large, it also reports this value in the error message.

Reported-by: Robert Elliott <elliott@hpe.com>
Signed-off-by: Jeremy Compostella <jeremy.compostella@intel.com>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/1466839230-12781-2-git-send-email-matt@codeblueprint.co.uk


[ Minor readability edits. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>