[rtl] Use outer generate loop for latch RF
[rtl] Use outer generate loop for latch RF

This matches the style used in the FF based register file. It gives each
register its own always block with a single enable rather than having
multiple registers with enables in a single always block.

Signed-off-by: Greg Chadwick <3e4c3d6d87c017d1a2fa161477653b4039c6b2fb@lowrisc.org>

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