[coreboot] Remove GENERATE_ACPI_TABLES

[Vladimir 'φ-coder/phcoder' Serbinenko]

By now most boards and OS don't run correctly if ACPI tables are not
supplied. Ability by user to enable/disable their generation is just
increasing configuration matrix for no benefit. So I propose to hardwire
it to HAVE_ACPI_TABLES.
I feel like in current config there are too many options of kind "Do you
want a working system? (y/n)" and they should be hardwired to right
answer rather than adding configuration.

http://review.coreboot.org/#/c/4609/