Update 40x vplans: interrupts, fencei, counters (since review meeting is done)

Created by: silabs-robin

The vplan review meeting was held and minor modifications to the vplans were done. (This should be ready to merge right away.)

For completeness, here is the changelog:

Interrupts

• Updated "killed instr side-effects" to check against iss (not assertion)
• Updated "killed instr side-effects" phrasing

Fencei

• Updated "stores visible" phrasings
• Updated "stores visible" change one of the tests to directed
• Removed test for self-modifying code that doesn't use fencei

Counters

• Added directed test to read mcycle
• Updated NUM_MHPMCOUNTERS configs to 0, 29, 1, 4
• Commented on "retirement timing" that rvfi can be used for comparison