efivar: Use struct guid_table instead of uuid_table

[imp]

Summary

uuid_table was the linux name. When libefivar was started, I tried to
make it compatible with Linux. However, that's no longer relevant: (a)
little to no Linux code was subsequently ported and (b) Linux compat has
eroded. This erodes it a bit more to cope with the uuid_t -> efi_guid_t
changes. This also moves a couple of functions around to reduce copying and
updates consumers for the visible parts of this change.

Sponsored by: Netflix

[kib]

lib/libefivar/efivar.c

45

I think it is more style-ish to have the intializator '{' on the same line as the variable definition.

lib/libefivar/efivar.h

83