⚠️ Rework hardware performance monitor (HPM) events

[stnolting]

The current HPM events are partially redundant and perhaps difficult to understand. This Pr tries to fix that by cleaning up the available HPM events.

This is the list of new and reworked HPM events with (hopefully) improved description:

ID	Name [C]	R/W	Event Description
0	HPMCNT_EVENT_CY	r/w	active clock cycle (CPU not in sleep mode)
1	HPMCNT_EVENT_TM	r/-	not implemented, hardwired to zero
2	HPMCNT_EVENT_IR	r/w	any executed instruction (16-bit/compressed or 32-bit/uncompressed)
3	HPMCNT_EVENT_COMPR	r/w	any executed 16-bit/compressed (C ISA extension) instruction
4	HPMCNT_EVENT_WAIT_DIS	r/w	instruction dispatch wait cycle (wait for instruction prefetch-buffer (IPB) refill; caused by a fence instruction, a control flow transfer or a instruction fetch bus wait cycle)
5	HPMCNT_EVENT_WAIT_ALU	r/w	any delay/wait cycle caused by a multi-cycle ALU operation
6	HPMCNT_EVENT_BRANCH	r/w	any executed branch instruction (unconditional, conditional-taken or conditional-not-taken)
7	HPMCNT_EVENT_BRANCHED	r/w	any control transfer operation (unconditional jump, taken conditional branch or trap entry/exit)
8	HPMCNT_EVENT_LOAD	r/w	any executed load operation (including atomic memory operations, A ISA extension)
9	HPMCNT_EVENT_STORE	r/w	any executed store operation (including atomic memory operations, A ISA extension)
10	HPMCNT_EVENT_WAIT_LSU	r/w	any memory/bus/cache/etc. delay/wait cycle while executing any load or store operation (caused by a data bus wait cycle))
11	HPMCNT_EVENT_TRAP	r/w	starting processing of any trap