bsp: cvitek: new design for pinmux

In the new design, we require the user to manually enter the
PinName (as a string) in menuconfig instead of being given
menu items to select.

The original method will lead to too many menu item-related
macros being defined in the code, causing ifdef and other
codes scatter everywhere in the driver code, which is
inconvenient to maintain.

The new design adds a pinmux driver module to manage the
multiplexing of pins. This patch provides this driver module.

P.S., the reason why users are allowed to specify pinname
in a string instead of the pin number is mainly because
the technical manual provided by the SOC manufacturer
does not have numbers for some pins, only names.

Signed-off-by: Chen Wang <unicorn_wang@outlook.com>
Reviewed-by: Yuanjie He <943313837@qq.com>
Reviewed-by: Shell <smokewood@qq.com>

bsp/cvitek/drivers/SConscript

@@ -5,6 +5,7 @@ src     = Split('''
     drv_uart.c
     drv_por.c
     drv_gpio.c
+    drv_pinmux.c
 ''')
 CPPDEFINES = []