Implement a SyncReadMem wrapper with explicit read, write, and read/write ports (backport #3228)

[mergify]

This is an automatic backport of pull request #3228 done by Mergify.

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Original PR Body

This PR implements a SRAM object, which wraps a SyncReadMem and instantiates a desired number of read, write, and read/write ports.

For example:

val memory = SRAM(UInt(8.W), 1000, 2, 2, 1)

generates a 1R, 2W, 1RW SyncReadMem with a size of 1000, and is controlled like so:

memory.rd(0).enable := timeToRead
memory.rd(0).addr := 3.U
// one cycle later after timeToRead is driven
fooData := memory.rd(0).readValue

memory.wr(1).enable := timeToWrite
memory.rw(1).addr := 100.U
memory.wr(1).writeValue := barData

memory.rw(0).enable := timeToReadWrite
memory.rw(0).isWrite := timeToWrite
memory.rw(0).writeData := bazData
memory.rw(0).addr := 50.U
// one cycle later when timeToReadWrite is driven but not timeToWrite
fizzData := memory.rw(0).readValue

Contributor Checklist

• Did you add Scaladoc to every public function/method?
• Did you add at least one test demonstrating the PR?
• Did you delete any extraneous printlns/debugging code?
• Did you specify the type of improvement?
• Did you add appropriate documentation in docs/src?
• Did you request a desired merge strategy?
• Did you add text to be included in the Release Notes for this change?

Type of Improvement

Desired Merge Strategy

Squash and merge

Release Notes

This SyncReadMem wrapper is instantiated using a new object, SRAM.apply, and invokes .write, .read, and .readWrite to generate a desired number of read, write, and read/write ports. This function returns a new Bundle wire containing the control signals for each requested port.

Reviewer Checklist (only modified by reviewer)

• Did you add the appropriate labels? (Select the most appropriate one based on the "Type of Improvement")
• Did you mark the proper milestone (Bug fix: 3.5.x or 3.6.x depending on impact, API modification or big change: 5.0.0)?
• Did you review?
• Did you check whether all relevant Contributor checkboxes have been checked?
• Did you do one of the following when ready to merge:
  • Squash: You/ the contributor Enable auto-merge (squash), clean up the commit message, and label with Please Merge.
  • Merge: Ensure that contributor has cleaned up their commit history, then merge with Create a merge commit.