sysview: take the timestamp from a BSP hardware timer where the core has no DWT

Cortex-M0/M0+, the WCH RISC-V parts and MAX3266x have no usable DWT cycle
counter, so their family.c provides SEGGER_SYSVIEW_X_GetTimestamp() from a
free-running hardware timer: a 32-bit general-purpose timer on ST parts
(sysview_stm32_tim2.h), SysTick-extended sources on the M0 families, the
core's SysTick-equivalent on WCH with the documented ordered read of the
split count registers (sysview_wch_timestamp.h), and a TMR on MAX3266x
(sysview_max32_tmr.h).

max32666fthr's DWT implements only watchpoint comparators (DWT_CTRL.NOCYCCNT=1
read live; UG6971 documents no DWT/trace at all), so SystemView's ARMv7-M
default read 0xE0001004 as a frozen 0 and every duration decoded as zero. The
TMR runs at 48 MHz (f_PCLK = f_SYS_CLK/2; Continuous mode, CMP=0xFFFFFFFF,
prescaler 1 - UG6971 15.2 guarantees TMRn_CNT readable while counting); TMR0
by default - present on every MAX32 part, unused by the examples, FreeRTOS
ticks on SysTick - overridable with -DSYSVIEW_MAX32_TMR=n. The family builds
SystemView with SEGGER_SYSVIEW_CORE_OTHER and sets CFG_TUSB_SYSVIEW_TIMESTAMP_BSP,
a tusb_sysview.c opt-in for ARMv7-M parts without CYCCNT where the BSP also
reports the rate via SEGGER_SYSVIEW_X_GetTimestampFreq(); the fixed-1MHz
microsecond contract is unreachable on a powers-of-two-only prescaler.
SEGGER_SYSVIEW_X_GetInterruptId() gains the ICSR.VECTACTIVE read for
CORE_OTHER builds. MAX32650/32690 use different GCR clock-gate names and stay
unported. Measured on the rig: seven host-timed 1.000 s gaps at
1.00044-1.00091 (median +0.05%).

stm32f0 refuses to configure SYSVIEW for stm32f070xb at CMake time: that
variant has no TIM2 at all, and the alternative was an undefined-reference
link error with no hint.

The shared hw/bsp/sysview_*.h join ci_select rule 16's hw/bsp file list
(cross-family build files, compiled only under -DSYSVIEW which no CI leg
enables), mirrored in the spec's rule table, so master's classification
guard resolves them on both axes.

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