Doc/mb/hp: Rename pro_3500_series to pro_3x00 series

The pro_3500_series was converted to a variant to include the Pro 3400, so rename the corresponding documentation.

Change-Id: I5977f223d6f004a801e163397d1c97febd7ee1d4
Signed-off-by: Vesek <venda.straka@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/85846
Reviewed-by: Nicholas Chin <nic.c3.14@gmail.com>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

Documentation/mainboard/hp/pro_3x00_series.md

@@ -71,7 +71,7 @@ region will be modified on shutdown. Cut the AC power or do a restart
 from the OS.
 
 **Position of FDO jumper (E2) close to the F_USB3**
-![FDO jumper position](pro_3500_series_jumper.avif)
+![FDO jumper position](pro_3x00_series_jumper.avif)
 
 ### External programming
 
@@ -83,7 +83,7 @@ The supply needs to quickly reach 3V3 or else the chip is also unstable
 until cleanly power cycled.
 
 **Position of SOIC-8 flash and pin-header near ATX power connector**
-![Flash position](pro_3500_series_flash.avif)
+![Flash position](pro_3x00_series_flash.avif)
 
 ## Technology
 

Documentation/mainboard/index.md

@@ -139,7 +139,7 @@ GA-H61M-S2PV <gigabyte/ga-h61m-s2pv.md>
 Compaq 8200 Elite SFF <hp/compaq_8200_sff.md>
 Compaq 8300 Elite SFF <hp/compaq_8300_sff.md>
 Compaq Elite 8300 USDT <hp/compaq_8300_usdt.md>
-Pro 3x00 Series <hp/pro_3500_series.md>
+Pro 3x00 Series <hp/pro_3x00_series.md>
 Z220 Workstation SFF <hp/z220_sff.md>
 ```