powerpc: Add generic PAGE_SIZE config symbols

Other arches (sh, mips, hexagon) use standard names for PAGE_SIZE
related config symbols.

Add matching symbols for powerpc, which are enabled by default but
depend on our architecture specific PAGE_SIZE symbols.

This allows generic/driver code to express dependencies on the PAGE_SIZE
without needing to refer to architecture specific config symbols.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220505125123.2088143-1-mpe@ellerman.id.au

arch/powerpc/Kconfig

@@ -759,6 +759,22 @@ config PPC_256K_PAGES
 
 endchoice
 
+config PAGE_SIZE_4KB
+	def_bool y
+	depends on PPC_4K_PAGES
+
+config PAGE_SIZE_16KB
+	def_bool y
+	depends on PPC_16K_PAGES
+
+config PAGE_SIZE_64KB
+	def_bool y
+	depends on PPC_64K_PAGES
+
+config PAGE_SIZE_256KB
+	def_bool y
+	depends on PPC_256K_PAGES
+
 config PPC_PAGE_SHIFT
 	int
 	default 18 if PPC_256K_PAGES