Add 20/26MHz Flash frequencies for slow/cheap flash chips on the Generic ESP board (#6552)

A number of non-genuine boards exist mainly from flea-bay sellers that
use under-sized and/or low quality flash chips which can not handle
a 40MHz FlashFreq properly.

This patch adds slower flash frequencies to the menu for generic ESP boards
so that these cheap knock-offs can be run in a stable manner, hopefully saving
some people a few headaches and keeping these boards out of landfill.

Author: ChocolateFrogsNuts

boards.txt

@@ -76,6 +76,10 @@ generic.menu.FlashFreq.40=40MHz
 generic.menu.FlashFreq.40.build.flash_freq=40
 generic.menu.FlashFreq.80=80MHz
 generic.menu.FlashFreq.80.build.flash_freq=80
+generic.menu.FlashFreq.20=20MHz
+generic.menu.FlashFreq.20.build.flash_freq=20
+generic.menu.FlashFreq.26=26MHz
+generic.menu.FlashFreq.26.build.flash_freq=26
 generic.menu.FlashMode.dout=DOUT (compatible)
 generic.menu.FlashMode.dout.build.flash_mode=dout
 generic.menu.FlashMode.dout.build.flash_flags=-DFLASHMODE_DOUT
@@ -4758,6 +4762,10 @@ wifinfo.menu.FlashFreq.40=40MHz
 wifinfo.menu.FlashFreq.40.build.flash_freq=40
 wifinfo.menu.FlashFreq.80=80MHz
 wifinfo.menu.FlashFreq.80.build.flash_freq=80
+wifinfo.menu.FlashFreq.20=20MHz
+wifinfo.menu.FlashFreq.20.build.flash_freq=20
+wifinfo.menu.FlashFreq.26=26MHz
+wifinfo.menu.FlashFreq.26.build.flash_freq=26
 wifinfo.menu.eesz.1M64=1MB (FS:64KB OTA:~470KB)
 wifinfo.menu.eesz.1M64.build.flash_size=1M
 wifinfo.menu.eesz.1M64.build.flash_size_bytes=0x100000
@@ -5778,6 +5786,10 @@ wifi_slot.menu.FlashFreq.40=40MHz
 wifi_slot.menu.FlashFreq.40.build.flash_freq=40
 wifi_slot.menu.FlashFreq.80=80MHz
 wifi_slot.menu.FlashFreq.80.build.flash_freq=80
+wifi_slot.menu.FlashFreq.20=20MHz
+wifi_slot.menu.FlashFreq.20.build.flash_freq=20
+wifi_slot.menu.FlashFreq.26=26MHz
+wifi_slot.menu.FlashFreq.26.build.flash_freq=26
 wifi_slot.menu.FlashMode.dout=DOUT (compatible)
 wifi_slot.menu.FlashMode.dout.build.flash_mode=dout
 wifi_slot.menu.FlashMode.dout.build.flash_flags=-DFLASHMODE_DOUT

tools/boards.txt.py

@@ -905,6 +905,10 @@
         ( '.menu.FlashFreq.40.build.flash_freq', '40' ),
         ( '.menu.FlashFreq.80', '80MHz' ),
         ( '.menu.FlashFreq.80.build.flash_freq', '80' ),
+        ( '.menu.FlashFreq.20', '20MHz' ),
+        ( '.menu.FlashFreq.20.build.flash_freq', '20' ),
+        ( '.menu.FlashFreq.26', '26MHz' ),
+        ( '.menu.FlashFreq.26.build.flash_freq', '26' ),
         ]),
 
     'flashfreq_40': collections.OrderedDict([