[Docs] Fix target feature matrix for PowerPC and SystemZ

The target feature matrix in the code generator documentation is
outdated. This PR fixes some entries for PowerPC and SystemZ.

Both have:
- assembly parser
- disassembler
- .o file writing

Reviewers: uweigand

Differential Revision: https://reviews.llvm.org/D71004

Author: redstar

llvm/docs/CodeGenerator.rst

@@ -1871,7 +1871,7 @@ Here is the table:
 :raw-html:`<td class="no"></td> <!-- MSP430 -->`
 :raw-html:`<td class="yes"></td> <!-- Mips -->`
 :raw-html:`<td class="no"></td> <!-- NVPTX -->`
-:raw-html:`<td class="no"></td> <!-- PowerPC -->`
+:raw-html:`<td class="yes"></td> <!-- PowerPC -->`
 :raw-html:`<td class="no"></td> <!-- Sparc -->`
 :raw-html:`<td class="yes"></td> <!-- SystemZ -->`
 :raw-html:`<td class="yes"></td> <!-- X86 -->`
@@ -1886,9 +1886,9 @@ Here is the table:
 :raw-html:`<td class="no"></td> <!-- MSP430 -->`
 :raw-html:`<td class="yes"></td> <!-- Mips -->`
 :raw-html:`<td class="na"></td> <!-- NVPTX -->`
-:raw-html:`<td class="no"></td> <!-- PowerPC -->`
+:raw-html:`<td class="yes"></td> <!-- PowerPC -->`
+:raw-html:`<td class="yes"></td> <!-- Sparc -->`
 :raw-html:`<td class="yes"></td> <!-- SystemZ -->`
-:raw-html:`<td class="no"></td> <!-- Sparc -->`
 :raw-html:`<td class="yes"></td> <!-- X86 -->`
 :raw-html:`<td class="yes"></td> <!-- XCore -->`
 :raw-html:`<td class="yes"></td> <!-- eBPF -->`
@@ -1931,7 +1931,7 @@ Here is the table:
 :raw-html:`<td class="no"></td> <!-- MSP430 -->`
 :raw-html:`<td class="yes"></td> <!-- Mips -->`
 :raw-html:`<td class="na"></td> <!-- NVPTX -->`
-:raw-html:`<td class="no"></td> <!-- PowerPC -->`
+:raw-html:`<td class="yes"></td> <!-- PowerPC -->`
 :raw-html:`<td class="no"></td> <!-- Sparc -->`
 :raw-html:`<td class="yes"></td> <!-- SystemZ -->`
 :raw-html:`<td class="yes"></td> <!-- X86 -->`