[tlul_sram_byte] simplify generate block
[tlul_sram_byte] simplify generate block

This commit does not introduce any functional changes - it just
restructures the generate block. I.e., instead of multiple generate
blocks with the same condition, we now end up with just one big block.

Signed-off-by: Michael Schaffner <a005a2d3342a687ea2d05360c953107acbe83e08@opentitan.org>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan