Remove MAYBE_STATIC_BSS and ENV_STAGE_HAS_BSS_SECTION

After removal of CAR_MIGRATION there are no more reasons
to carry around ENV_STAGE_HAS_BSS_SECTION=n case.

Replace 'MAYBE_STATIC_BSS' with 'static' and remove explicit
zero-initializers.

Change-Id: I14dd9f52da5b06f0116bd97496cf794e5e71bc37
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/40535
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/lib/program.ld

@@ -112,7 +112,7 @@
 }
 #endif
 
-#if ENV_STAGE_HAS_BSS_SECTION && !ENV_CACHE_AS_RAM
+#if !ENV_CACHE_AS_RAM
 .bss . : {
 	. = ALIGN(ARCH_POINTER_ALIGN_SIZE);
 	_bss = .;